My choice of edgeguarding depends on the character.
For Ness, Yoshi, and Falcon, I like to mess them up by dropping off with a Nair. There's little risk to doing it. Either they deal with me, risk losing momentum, and most likely fall their death, or they try to find some alternative safe path back to the stage. Either way, it's safe to at least go for it. If you hit them during their double jump you can net a stock off of it easily.
For Diddy, I'll jump offstage and flamethrower him. It's sooo effective at gimping his recovery
For Bowser Jr, I do the same thing as diddy. Only if he recovers low.
For Fox, first I see if he's bad. If he phantasm's back to the stage in a predictable way, I punish that with smashes. Lots of smashes.
If he decides to go for firefox, I'll occasionally run off, flareblitz towards the stage, and try to stage spike him out of it. It's so satisfying to pull off.
For Rosalina, just Dsmash her out of her Up B. Her head pokes above the stage right before she snaps on. If i have a good read on her angle, i'll just intercept it with a fair. Offstage fair kills at crazy percents.
For Pikachu I-- Pffff, who am I kidding... you can't gimp pikachu... he'll just... he'll just...