I leveled as Veng/imm hybrid until 44 then switched over to a rage build. I didn't have any problems tanking when necessary and did decent damage as vengeance. I lvled as Immo in beta and found veng to be faster.
I used the ability that refreshes the cooldown on saber ward. Between that, choke, throw, and the typical interrupt I had no problem with him.
Oh, and this was with Quinn using rage/imm spec.
Personally I'm specced rage/immo at the moment and will probably switch over to rage/veng at some point soon. I'm typically not #1 on DPS all the time but it has happened, but I am usually top 3-5 damage and top protection too. Oh and I just hit 50, so only 1 piece of pvp gear thus far. I was a hybrid vengeance/immo spec for a while and I just wasn't enjoying it as much. I think it's just up to you. If you're grouped consistently for pvp it may make sense to go immortal. I'd say try both specs in groups and solo and then make a decision which type of gear you want first.