As mentioned before Shulk is an interesting one because he outranges you, but none of shulk's things are safe on run in shield(so that he lands right in front of you). also his nair, his best aerial is easy to perfect shield. So you can literally just run in, perfect shield most of his spacing options and catch his landing.
Falcon's pretty easy I think, he has a reason to go in, you don't cause you have a projectile and you have a down B to charge. Space him out, big sword beats muscular leg, pivot ftilt and things of the sort help when he is trying to approach you with nair and what not. SH Bair is also a really good tool to just say "no" to him a lot.
ZSS: ZSS is, for the most part, better falcon, I can't help too much because every ZSS player I've played has just been impatient and OOOH Nair! Paralyzer grab!/so I just space them out. I can't help if that ZSS has more brainpower than that.
Ike: one of cloud's easiest MUs, you have a bigger sword and faster frame data, just don't do any stupid approach and you should be fine. again, spacing Bair is godly here. Don't fall for any of his autocancels!.
Sheik: as said before, each sheik is different. I kinda like Cloud Sheik but it can be really grindy. Always keep needles in mind(so if possible play in somewhere with platforms). You could watch M2K play some sheiks and see where he screws up and what he does right. Nair is really good at not letting sheik go in. Try to meet her at a comfortable distance in air-air situations. Don't lose your patience if she stays grounded(again, another reason to pick platforms). If he uses needles a lot, try to see what his option out of charge is (He can shield, roll, needle fidget into an attack or run away, shield jump) and try to read what he is going to do out of charging needles and punish him for what he does