If you want to group all the time, obviously tank spec. If you want to mostly solo, I'd go vigilance. Thats not to say you cant solo in tank spec, it will just be a bit slower. Its also not to say you cant tank in dps spec, you'll just be a little squishier. If you're curious, I'm leveling as vigilance and can comfortably do most heroic 2+ missions with Kira.