The most rewarding one would be a minion master. Necro/rangers do well, they have their pets die and summon minions from those (then they rez and repeat) if they can't find fleshy creatures.
necros are the best pve class. ne/mo to be specific. get a warrior to kill a couple of creeps for starters, then heal area and veratas sacrifice and maybe blood of the master and your in the money.
Debatably. You seem to have a lot of experience as a minion master, there are other builds, and they may not be too pve geared. As for efficiency, minion masters have tanks, as well as tons of dps. When your minions are about to die -just cast death nova and have them deal some more damage.