Agree w/ sphnyx to a point. PVP you have to hit your opponent - preferably first, so AGI is very important.
Have Siren in the back row since she's not very fast, but would be very useful during the Full Squad 3rd fights. Kidaj's silence skill will help as will Wasteland's demoralize skill.
When you finish your Endel Oni, drop him between your 2 Primarchs. With those buffs, his skill will cause many opponents troubles. Until then, put your Obliterator in the sweet spot.