It was so long ago, I barely remember.
I think it may have been either Kouhai Mario or Brutal Mario.
Considering the amount of nostalgia for daigaidai's hacks and how much of an impression they've left on me, to the point where a lot of little things about those hacks still reflect in my preferences for SMW hacks and even how I design levels, years after I've played them (and it has easily been about 8 or more years since the last time I've played one of them), it may very well be Kouhai Mario. That one hack holds a very special place in my heart, for being probably the first hack I've ever beaten, more than once no less (although I'm pretty sure back then I used savestates). Same with his other hacks.
Anyway, Brutal Mario is also a hack that I've played in my early years, and it's kinda impossible to not have played it if you lived at the time it was on the height of its popularity. It was kind of impossible to not come across it at some point if you've watched videos of SMW hacks back then.
Hacks from my early years also include some of the VIPs, :𝖯:𝖯:𝖯, SMW Yeah!, Hakurei Adventure (I think that was the name) and some more hacks I can't remember well because my memories are just foggy.
It doesn't help that I've just played too many back then, like a whole lot.
The first western SMW hack I've played I also don't remember well, because I've just played a lot of stuff back then and not only that, but it was just too long ago, as I've mentioned, I can remember what I've played back then, but the exact order can get confusing.
But... I think the first western SMW hack I've seen was Panic in the Mushroom Kingdom (though I'm not sure), I don't recall that being the first one I've played though.
I remember playing stuff like Ketchup Adventure, Mario Gives Up 2 (I've played 2 first), Mario Gives Up, Drama Mistery, ASMT, Saph and the Great Rebellion, World of Illusion (that's an early one, I wonder if it was the first non JP hack I played), some one-level hack where you play as Yoshi and whose name I forgot, a lot of one-level hacks from contests (except I didn't really know they were from contests at the time), a hack called EVW, A Simple Mission (I actually don't remember if that's the name, it was a hack by WhiteYoshiEgg and the acronym was ASM), Luigi and the Island of Mystery, The Muncher Run by Ersanio and that's all that I can remember well.
It's a shame, I'd love to go over literally everything that I played back then (or most of it), it would just be quite great, a nice retrospective. It's a big part of my life honestly, pretty nostalgic and a lot of hacks though aged poorly, just shaped my preferences for SMW hacks and even platformers a little bit in many ways. It's easily my favorite era for SMW hacking, I like the renaissance of ambition, experimentation and difficulty we're getting recently with stuff like YUMP (which is good for the most part), JUMP½, slurdgery, mice, 2 mice and whatnot. But I seriously love how passionate those old hacks felt, even when at their most janky and weird, there was an air of simplicity and ambition that I really liked.
I like how in many old hacks, when there were custom BGs and FGs, often the status bar colors would change, nowadays it would be considered a flaw and there's a lot of emphasis on consistency and making things look sleek and professional. Back then, I wouldn't bat an eye at what's consistent or not, I just loved when there were different graphics and music, especially when it looked really different from vanilla SMW, because it was just mindblowing to me seeing that, and the different colors on the status bar actually looked cool to me, which is silly to imagine now.
There was an unexplainable mystique to almost every SMW hack for me back then, and I know it was more because I was just new to that, but wow, it was just a great first impression. Like seriously, despite not remember the specifics of many hacks I've played back then, I have great memories of how I felt at the time and I'm sure if I managed to find them again, a lot of the memories would just jump back to me and make me feel really emotional (because I'm just super nostalgic and melancholic nowadays).
But that's a story for another day, I don't want to make this post even longer.
Хуй войне!
桐生会FOREVER #ThankYouCoco / Rest in peace, Near, thank you for everything