I like running or jumping off the stage into nair and downsmashing as they are recovering (separately, of course). If you nair them off stage and they are low enough% and/or DI towards stage, it combos into an up-b meteor smash. Grabbing onto ledge and dropping into doublejump bair is also a really good technique, but I haven't really played around with it too much. Upair, dair, and fair are unviable off stage and downsmash is pretty much the only move you'd ever want to use on stage to ledge guard.
If you grab ledge and they recover above you, drop-double jump-fair works pretty well.
EDIT: I also like to down-b into dive kick to ledge guard sometimes as well. If you jump cancel the dive kick, it's perfectly safe. However, if you miss, you give up stage control.