Well, when I first started making levels, LemEdit and CustLemm is all there was. I wasn't really any great at making levels back then though. Once I discovered Cheapo, I used that almost exclusively for the longest time - it was only when I realised that Cheapo had well and truly died out and wasn't coming back that I made the switch to Lemmix (actually, I used LemEdit + WinLemm for my first release after switching away from Cheapo - I speak of course of "Ji Hoon's Lemmings Remake" here, the only large pack I've released without using the Lemmings Plus branding) - I believe my Lemmings Plus 3 was one of the last Cheapo packs to be released? And for those who didn't know, I was even planning on making a Lemmings Plus 4 in Cheapo, but that project never got very far (although some of the LPDOS levels are remakes from it - most notably, No Time To Die and Death Row).
With Lemmix being accurate to the originals, but with handy features like savestates and replays that are invaluable for testing level designs and concepts, it just can't be beaten IMO. Not to mention it's open source, which means I can easily compile the all-in-one player apps for my level packs (and as you know, my level packs are almost inevitably on the very large side - there was the Ultimate Challenge series and a couple of individual small packs, but with 5 (
soon to be 6) large packs released, you can see which type I go for more often) - and include custom tweaks to the mechanics while I'm at it (the most notable one being the instant bombers in later versions of LPDOS and all versions of LPII). There's also that I don't have to worry about if a future update will break something in my levels - because I can just compile a player which has the exact mechanics, glitches, quirks and all that I was working with when I made the levels. Being able to use the editor I'm most used to (except for maybe the Cheapo one) is a bonus.
Lemmini just isn't really my style. I feel it's a bit clunky and the mechanics a tad on the weird side, plus, I like the challenge of working with the original low-resolution (it also allows me to hide my complete lack of artistic skill a bit more xD). Not to mention the f***ing annoying sound glitch, where Lemmini sometimes lags (then super-speeds to catch up to where it should be) when trying to play a sound - this alone is pretty much a dealbreaker for me, even without the other issues. (These reasons are also why I don't even release Lemmini ports of my packs - because I simply cannot be bothered testing the levels in Lemmini. Yes, it has replay, and yes, back in the Cheapo days that's how testing was done, but these days with Lemmix available, it's hard to go back to that.)
Lix doesn't work very well on my PC, as I explained in another topic. I remember it (or *some* fan-made multiplayer clone by a member of this board, anyway... the name L++ rings a bell...) running better on an older PC I had; though I never tried the level editor much, I just played a few online games. Though admittedly, multiplayer in almost any game isn't really my thing, the only game I really do multiplayer much is Tekken. Another thing I'm not too keen on with Lix is the new skills - well obviously, I could just make levels that only use the classic 8, but yeah, it does mean more skills to familiarise myself with exactly how they work; not to mention getting used to exactly how the existing ones work in Lix.
So yeah. Lemmix for me; I would be open to working with Lix if it worked for me (though with the flexibility it allows, I'd probably ultimately stick with Lemmix for major packs, but that doesn't mean I wouldn't release a few smaller packs on Lix). I prefer to stay away from Lemmini. The other thing I have considered is making my own engine - a lot of work, but it might be worth it for being easier to customize things than Lemmix (which, while open source, is still not my own code and thus I don't know all the ins and outs of how it works - it's not even in a language that I'm overly familiar with).