What matchup(s) do you utterly detest with your main so much that you keep an extra character/team for it? Applies to all competitive/FGC-approved fighters.
Big one for me is Felica in VSav. I keep a Sas on hand do deal with her. I know there’s others, but fighting her feels so damn oppressive.
I’ll counterpick if I know how to play more than one character. I counterpick often in SFxT and InJustice. Though in games I only play one character like Blazblue I curse the heavens and clutch my teeth whenever I get a bad matchup.
Depends on character popularity. If you go 7-3 or worse against a common character, you should keep a counter on hand because you’ll be consistently handicapped. Toughing it out is silly when you’ll easily fight 2 or more of said character in 10 random matches.
How often you play characters that lose 2-8 or 3-7? A dumb MU is even worse because there’s no way to improve it. At least you can get good with your secondary.
In 3S I have a pocket Yun (SA2 lol) for dealing with Makoto/Chun. Not really because those matchups are hard for Akuma; I just find them super annoying.
I like MvC3 Viper, but 70% of the reason I devoted time to learning her is FUCK DORMAMMU
I wish I had a counterpick for MvC2 Storm. Fifty characters and that bitch is awful no matter who you pick.