I have never been to the minus world. I didn't know about it until my NES stopped working and you can't do it in SMAS so I'm stuck. But if I ever get a Rev then I definitely want to try it.
I like the plus world in Lost Levels. Where else can you get attacked by Lakitus and Hammer Bros. and grab a flagpole-- all while being underwater. But the last level could have been a ton better. I can picture in my head 7 Bowsers in one level that you have to get past by using trampolines, avoiding while underground, avoiding while fish jump and bullets fly past you, and also on tree tops. My favorite idea would be a castle where Bowser shows up behind you at a certain point and chases you through the rest of the level with fire breath and everything until you touch the axe. Excuse me for daydreaming again.