I play multi very rarely, usually only in the rare occasion when I'm invited at a LAN party, so I don't really hone my skills much (I do play single player shooters, but multi is an order of magnitude harder). That said, I'm usually at my best with a precise, powerful weapon. I remember a vacation in Brighton, many years ago; me and my friends were chronically bored, so we'd spend many, many hours (and pounds...) in a local LAN-cafe playing Quake 2 against the locals. I have fond memories of sniping the hell out of everyone with the railgun, and of other players swearing whenever I let the blue trails fly.
There's no role in which I
completely suck, and I'm at least half-decent with all other weapons, though I've never really liked rocket launchers (I'll use them if nothing else is available, but I'll switch to something else as soon as I can).
Edit: oh wait, there is one thing in which I'm absolutely worthless - grenades. I can't seem to judge the throwing angle, and always somehow end up blowing myself up. I usually just ignore their existence and get on with my life.