Ok, favorites. I guess basically anything that isn't the run-of-the-mill "hold back the crowd, let a trailblazer does the rest, release the crowd" level.
There are actually a good number of these levels now that I look back.
"It's Hero Time!" -- who doesn't like the "1 of each" concept when they first see it? I guess it's sorta a "hold back the crowd..." type level in a way, but the solution's elegant in a way.
"Postcard...." -- same deal.
"Heaven Can Wait..." -- a nice simple example of "the pit" technique. Due to the order I played the levels, this is the first level where I discovered the technique, and that technique quickly prompted me to replay many of the earlier fun and tricky levels for 100%.
"It's Lemmingentry Watson" -- another "elegant solution" level
"Compression..." -- neat idea, although I must concede that I think I might've sought outside help for this one.
"Poles Apart..." -- interesting concept
"No Added Color or Lemmings" -- Another level with a neat solution. This one took me a while since I didn't know yet at the time that you can release stoppers. I did eventually figure you need to use the stopper, and somewhat accidentally found out the secret when I was merely mucking around with the idea with using a mine + bash tunnel going underneath the blocker to release the crowd.
"Down, Along, Up..." -- I have to admit this can be kinda a pain at times, but it's kinda neat. Another one where I remember stumbling upon the right way to do it by accident, when the stopper was merely a desperate attempt to hold back a disaster and I built the "wrong way" accidentally...only to see the stopper did its magic.
"The Great Lemmings Caper" -- Anything with 2 lemmings is interesting since it's guaranteed not to be the run of the mill "hold back the crowd" thing.
"Mind the Step" -- the only one Lemming level. Though I have to say it's rather tedious to actually complete.
"Just a Minute..." and "Just a Minute Part 2" -- actually these eventually ended up being levels that kind of disappointed me, when I realize from other people's solutions that you don't need any cleverness to squeeze in enough time. You won't believe the weird stuff I did in this one in an effort to buy extra time that I thought you need (like send a climber up and ahead to dig then try to bash part of the right end before the basher from the left gets there). I think this could've been more interesting if they were more careful about making the solution less straightforward.
"Lost Something?" -- just kinda humorous. Did took forever mucking around for the exit though. I can't remember if I eventually sought outside help on this.
"King of the Castle" -- I just liked the idea that you have to do everything you need in this level using builders, and only 20 at that. When you first look at it you're like, whoa, only 20 builders? But after a good number of attempts it's no longer too hard.
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I also like the 4 "special graphics" level, but only for the graphics and alternative music. The puzzles themselves are as run-of-the-mill as you can get.
I did like "Not as complicated as it looks" for the witty idea. It's stupid puzzle-wise but you have to admit the concept fits in the "Fun" series very well.
"Steel Works" was kinda nice, at least in terms of the setup work you need to create a safe landing place [ignoring the fact I later found out from others you can merely just start building right at the landing spot to get the job done]. The rest of the level is quite tedious though.
"Going Up..." -- I just like its concept of having to take a route up on the ceiling.
That's all folks I think. I never had "Oh No" until recently but the "Oh No" levels do sound interesting. "Save Me" isn't on the list because it was the only level in the original set I kind of never complete until much later (somehow I never figured out the concept of "stoppers on bridges" on my own, and I think at that point back then I was too eager to get to the end so I just went online for a password to skip to the next).