If you are playing exclusively by yourself I imagine rogue probably would be. You either stomp other classes, or put up a decent fight. When I played a rogue there were some tough classes, but never a “I have zero chance of beating this” kind of deal. In group PvP it varies depending on the other classes involved.
There is no “overall” best class, but classes do excel at different things, and there are differences based on specs.
i.e. warlocks and shadow priests(and sometimes rogues) are good 1 v 1 classes, warriors, mages, healers, and shamans excel in groups and BGs, stealth classes have advantages in world pvp, druids are best flag runners for BGs, etc etc etc.
Open world - Warlock, shadowpriest, mage, rogue, druid
BGs - Warlock, Shadowpriest, warrior (if you’re being supported by dispels and heals), Ele shamans are pretty good too.
Prob in that order or close to if you’re talking about overall capability to win fights.
Doesn’t mean other classes are worthless/don’t have their favorable fights but these classes will pretty much dominate their respective areas. Prepared to be miserable if you aren’t playing a lock or priest or warrior (running with friends) in bgs.
Warlock tops charts 24/7 from what I remember and they are beasts in world Pvp. Shamans are also good but in instanced Pvp they may be prone to interrupts a weakness warlock’s lack