Honestly, I'd say that SW is fine. I've run with both marauders and juggernauts, Juggs mostly in tank spec. Some juggs suck at holding aggro, others do it perfectly. 90% of the game is down to how you play. If you're good with your class, you'll be able to clear content. If you suck, your dps are going to pull off of you like I do with the bad ones I run with. on the same thread, there have been powertechs I pull off of as well, and my healer friend has mostly hated healing them, feeling they're squishier than other tanks. Maybe that's just his experience, maybe not.
All in all, any of the three tanks is more than feasible to tank any of the currently available content. My suggestion, find some friends who play or make some in game, start/join a guild with them and screw the other guild who are rejecting you simply due to your class choice. Hopefully, they'll invite a powertech who has no idea what he's doing and they will endlessly wipe on their ops attempts.