i dont like either of them.
but if i have to choose its orion couse he got nice damage%.
for me best pet for pvp is slag. it got awsome damage, hp, speed and stun.
best for soloing tombs, searching for bael etc is abaddon. it has great speed boost, great damage and nice aoe damage skill.
for elites colton is very good, it gives you nice int, damage and party crit boost.
arcane pets are the best but hard to get, so among easier to get pets here you go.