I never really played with the Oh No! More Lemmings tilesets until recently. Truthfully I like them all, although I do feel that Snow is somewhat 'boring' in a way. Bubbles is a pretty surreal tileset that is fun to play with, but I dislike it from a design standpoint because of the lack of steel pieces. Brick is good for making 'precise' levels, but the awkward trigger areas can be problematic. Rock is the 'Dirt' of Oh No! More Lemmings, and has quite a ghostly beauty about it - has a fairly unique take on water too.
Though I'm late to the party, my favourites are Crystal and Marble, for different reasons:
- Crystal: Has a dark beauty about it and is kind of 'peaceful' in a way. I absolutely loved making Crystal Caves out of it! Hard to make precise levels though and the lack of 'dead zones' outside of water make things tricky sometimes (although Crystal isn't unique in this problem).
- Marble: A very nice tileset from a design perspective. Very easy to make pretty-looking levels out of it, and the shredder trap is such a compact and versatile 'dead zone' to keep Lemmings away from where they shouldn't be.