I'm going to "cheat" by including SMKAS and ASMKC in some of my answers, although I'll try to always provide a "CDX-exclusive" answer as well.
Best victory (overall or in a specific mode):I don't have a particularly good answer for this, but one victory that comes to mind is Neo's win in GP 2016. He had already lost the overall title to ScouB, and had a surprisingly weak GP GS (with losses to ScouB, Geo, Jey, Sami, and Chollet). Despite this, he went on to absolutely demolish everyone in bracket, with 2-0 vs Chollet, 3-1 vs Geo, 4-0 vs Wild, and 4-0 vs ScouB to take the gold. It has added value in retrospect considering that the only gold medal that Neo has won since then is BM 2017.
Best TT edition:Uh... shoutouts to the absurdity of TT 2018, I guess?

In terms of strength of the field and intensity of the KO stage, I'd give 2021 the nod (although I expect 2022 to be even better).
Best MR game:ScouB vs Sami in the MR 2018 final is iconic. Hard to top that, although I think that my battles with Mario in the last couple years are worthy of a mention at this point.
Best BM game:BM 2016 final.
Best GP game:Not sure, there have been several very exciting GP finals.
Best comeback ever:ScouB vs Sami in the MR 2018 final, once again.
Less deserved victory / Biggest robbery:No idea.
Most unexpected/surprising qualification:I think that Lucas qualifying for BM 2010 at only 9 years old will never not be surprising. Also funny that he qualified off of a round-differential tiebreaker at his father's expense.
Most deserved/funny elimination:Aron failing to qualify for TT 2019. There was no conceivable reason that such a strong TTer should fail to qualify, but Aron found a way to do it and in style (finishing 20th).
From what I've heard, Bab's elimination in BM 2009 Top 16 also deserves a mention for Drew playing with his back to the TV in response to Bab's shittalk prior in the day/week.
Biggest "gift" of history:I think to evaluate how big a gift is, we need to take into account the stakes and moment of the match in which it took place. With that in mind, I think it's very hard to argue against Sami's VL2 gift in the MR 2018 final. That being said, I think that Jarmou's GV1 gift in MR 2021 upper Ro16 deserves a very honorable mention given that it was completely unprompted on lap 5 at double match point in a match involving two players who had never made a QF/Top 8 in MR before.
Most surprising opponents in the same final:I think that results tend to be sufficiently consistent at CDX that it's rare for there to really be any big surprises in who makes it to the finals. With that in mind, I'd say that the most surprising final lineup was Mario vs me in MR 2021, especially if you're someone who didn't pay attention to or value SMKAS results.
Best championship edition (all criteria: venue, game quality, organization…) :From what I've heard, 2017 was incredible from an organizational perspective and sounds like it was an extremely fun event.
Worst championship edition (same criteria) :I don't know what conditions were like in the CDF era (I suspect 2006 might have been particularly "rough" for obvious reasons), but it seems to me that 2016 had particularly bad circumstances, especially with regards to the ridiculously hot and noisy venue.
Your best personal TT memory:Hard to pick a single one, but I think that the best one might have been when I qualified for the 2018 QF. I was very, very nervous while waiting for the results to be announced because I really wasn't sure whether I had qualified or not. The minutes of anticipation made me very, very happy when Patrick called my name in 7th.

Special shoutouts to the final track of ASMKC 2022: I had been playing extremely well throughout the KO stage, and pulled off a balls-to-the-walls GV2 to edge out Karel by "02 and win my first ever championship gold medal.
Your best personal MR memory:Although I've been really enjoying my MR duels with Mario since SMKAS, my best personal memory can't be associated with those because I ultimately fell short and got silver to him in both 2020 and 2021.

Instead, my answer is my 7-6 win over Neo in 2021 upper semis. That match contained all the ingredients for an incredible memory: I came back from a 6-3 deficit with a combination of great items and execution, pulling off multiple do-or-die moves to stay alive and ultimately win over one of the all-time greats.
Your best personal BM memory:I don't have any particularly strong answer to this. Two non-CDX answers come to mind. The first is my 5-2 win over Jey in SMKAS upper semis, in which I successfully implemented a strategy to grind him down over the course of what might very well have been the longest 7 rounds of BM ever played in a championship KO stage. The second is my 4-3 win over Drew in the ASMKC 2022 upper final, in which I used the exact opposite approach and managed to blitz Drew and catch him off guard just enough to snatch the win. Unfortunately, in both cases I lost the rematch later in the bracket, finishing with a bronze at SMKAS and a silver at ASMKC.
At CDX, my best memory is probably snatching a draw in 2018 GS against Neo before he even had a chance to really figure out what was going on.
Your best personal GP memory:Without a doubt, my match against Takashi in 2019 Top 16. What an electrifying moment! It'll take a lot to ever top this, even though I lost that match.
You might think that my bronze medal from 2021 should be up there as well, but honestly I have very mixed feelings about it. My path to bronze felt very lackluster: I beat Jarmou 2-0 in quarters and Wild 2-0 in semis without any fanfare, as I felt that neither opponent played to their "real" level, and I heavily benefited from Wild's upset on Neo in quarters. I then lost two cup 5s to Geo and Jey, which left me with a rather bittersweet medal.
Your worst personal TT memory:I don't think that it impacted me as much as it "should" have, but my answer to this must be the final track of ASMKC 2020, with both Sami and I on the verge of elimination. I went for and landed the GV1 PJ on lap 2 (after mistakenly thinking that Sami had done so on lap 1), then immediately crashed the first corner of lap 3 and proceeded to lose the track and the gold. It would have been an incredible story if I had managed to keep it together, but so it goes. (My first ever championship medal would have been a gold after a grueling fight in which I survived by a thread for ages against Sami and Karel.)
As for CDX, my worst memory is crashing on BC2 in the 2018 QF. I lost 3-4s by smacking into a thwomp inside the maze (for some bizarre reason), which cost me a qualification into the semis that I would have otherwise been very likely to achieve.
Your worst personal MR memory:Nothing too egregious in this mode, but I do recall being frustrated by the way my match against Conor played out in 2018 Top 16. I had only just started to develop my MR tactics in 2018, but I had pulled off a couple cool moves to clutch a 3-1 win against him in GS. Unfortunately, the Top 16 match didn't align with that earlier result at all, and I lost 5-1 in a match where nothing seemed to go my way.
Your worst personal BM memory:I don't have anything significant that comes to mind. If I had to mention something, perhaps I'd bring up Neo forcing me to play map 1 again instead of map 4 against Narnet in 2016 GS.

Worth a mention as well is losing out on $1500 for failing to beat Drew a second time at ASMKC 2022.
Your worst personal GP memory:This one is probably my worst championship memory of all: while playing a Star Cup against Matt in 2018 GS, I thought that I had finished after crossing the line on lap 4, and drove straight into the deep water. By the time I realized my mistake, it was too late, and I went from a comfortable 1st to ranking out. This single mistake led to a spiral of consequences, which culminated in me getting eliminated by Wild in Q2 barrages. In turn, that elimination meant that I failed my two major goals for 2018: qualifying for every mode and finishing in the overall Top 10.
Your biggest achievement / the peak of your championship career:Hard to argue against winning the overall title in 2021.
Your worst championship performance / biggest disappointment:The chain of events caused by the single mistake against Matt described above. I hope that will be my last failed qualification ever, and not for lack of participation.
The game you could have won if you had played it instead of being eliminated just before:This sort of speculation is "dangerous" in that you never know how things would play out, but my answer to this would be the 2019 MR QF that Geo lost to Harold immediately after beating me. Watching that match, I can't help but feel disappointed in Geo's play and imagine myself having at least put up more of a fight against Harold.
Alternatively, I think that if I hadn't made that mistake on BC2 in TT 2018 QF, then I would have had a very reasonable chance of making the final.
The championship (or mode) you didn't play, but wish you had played:I have played in every single championship / mode that I possibly could. That said, I would have loved to attend one of the La Suze CDMs.
I also would have liked to attend the first ever ASMKC in 2019, but it wasn't possible for me at all due to uni/work scheduling.
The championship (or mode) you played, but wish you hadn't:None.
The best championship you have attended:I think that nothing will ever re-capture the magic of attending my first CDM in 2012. It was a truly unique and special experience that will forever live in my heart. This isn't to say that other championships haven't been some of the best times of my life, but the fond memories of that particular week are ones that I cherish just a little bit extra.
The worst championship you have attended:2016, both for the general CDM circumstances and my personal ones. (Staying at Ours' place was pleasant, but sleeping far from the venue is a major drawback that I now avoid as much as possible, and that year I wasn't able to stay for the closing ceremony.)