Do girls care what kind of underwear guys wear?

no, because you don't really see it, and if you do, it's only for a bit before they're off

As long as it's relatively clean, not riddled with holes and the right size, no. Style doesn't matter.

I used to just wear plain boxers I would get from the gap or something, but I've had multiple girlfriends complain about it. They said they look like "old man underwear" and wanted me to wear boxer briefs.

My current gf says she wants me to wear no underwear at all but FUCK that