I think Sheik is the worst for Samus. And a smart/consistent space animal. But like there's an entire list of characters that **** Samus up in higher level play.
-Falcon
-Ganondorf
-Sheik
-Marth
-Peach
-Fox
-Falco
-Jigglypuff
I really think it's a matter of whether your opponent knows their character's match ups. They be a really solid or good, say, Marth; and get that *** tapped because they don't know how to fight a gay Samus very well.
I've played so many Marths that fell for my tricks, but I'd be watching **** heads all day on other people. But then some of them learn the match up and tada! I get smacked.
But personally my worst match up is Falcon. Missiles mean nothing to him, and he can close the distance between the two of you very quickly, plus small stages mean depressingly quick kills against Falcon unless you know how to escape those combos.
I have two Falcon players in my crew. I used to easily beat them, to the point where it'd be embarassing, but now I have to be absolutely at my most alert when I play them; otherwise I'll get two stocked. Just because they realized how to utilize their character's advantages over Samus.
I find the only way I can **** them is if I control platforms or stay close to the ledge and get them off. When they go off the stage, they stay off. Except Frozen, because he techs as well as anyone out there which always catches me offguard.
I generally employ that same strategy versus Marth as well. Marth is a joke when he's trying to return againt Samus, unless you let him sweetspot the ledge. And it's easy to return versus him if you're knocked off the stage.
The only Marths I fear are the ones who treat every edgeguard like it's their last - they go entirely too far off the stage for that last swipe at you when you least expect it, barely nip you; and get the stock and return to the stage. But besides that Marth is much easier for me than certain other characters.
Peach is a character I recently started getting better against. If you're not dumb enough to fight her on the ground, her most damaging move is useless. In the air you can take advantage off your longer reach, and if I get above a Peach I often use downair and see how they react. If they don't shield they get three or more downairs into a sex kick, if they do shield; then I hope I land behind so I don't get shielgrabbed. >_>
The only thing I hate about that match up, is that she can float so high above you, which makes edgeguarding irritating. Homing missiles only go so high. >_>
A guy in my crew named cmart mained Jigglypuff, and I never won a single match against him. Of course he knew my game inside out because he also used Samus, but it was pretty traumatizing. Everytime I went off stage I'd die because he jumped straight into my bombs.
If I ever used a missile it got WoPed or crouched under. And I was afraid to use anything slow because I'd get rested more often than not. Of course though this is probably just me. But another Samus main in my crew has a bad Jigglypuff record as well. In more than one tournament he was 2-0'd by a Jiggly named Aero.
But yeah it may just be us. Because while cmart ***** me, he'd never beaten Jasona's Samus whenever they played, though they had close matches. So I guess it's more strategy in that match up than overall better character.
Against space animals I'm so randomly bad. The only way I can beat them, is by controlling the platforms and gimp killing like a mother****er. Same as with Captain Falcon for me. Lots of tilting, lots of downsmashing, lots of upthrows and gay edgeguarding.
Another match up I kinda like a Sheik. You can **** her up with platforms, though your missiles mean **** to her. She's somewhat easy to edgeguard unless you don't beat that teleport. All I really hate about the match up is being shield grabbed.
When I get needles thrown at me a lot, I start to become impatient and try to rush the Sheik, and then improperly space an aerial and get shield grab. The Sheik I play loves to shield grab, he shows no mercy with his Sheik ways. I get ***** by needles when returning and also the entire match. So I actually really, really, hate this match up, but I like it when I downsmash a Sheik off the stage.
And I hate Ganondorf. I've died unexpectedly from four-five hits numerous times. >_>