If your xbow, i think probably bard is better. As crossbow have great range and great damage, you can do some nice hit and run.
As for warlocks, i'm afraid you'll have to go a bit closer to the enemy to debuff them. Not a bad sub IMO, but maybe warlock sub will suit dagger rogue more ( debuffs + sleep/stun + DD on + prick = 1hit KO for most builds )
You may consider cleric for tanking power, but my advice will still be bard.
Just my 2 cents tho
