Any FO will do, it really depends how you want to play them.
FOmar is good as an all rounder, as he has ok nukes (especially with Gifoie) and strong melee, with extra range on his Shifta/Deband.
FOmarl is really good as a support and pure melee FO, as she has some unique options that make her stronger than FOmar in various situations, and her range makes it nice and easy to support.
FOnewm is the best nuker by far, he's the king of solo. He's alright at melee, but both human FOs are better at it for multiplayer.
FOnewearl is basically FOnewm but without melee capabilities and weaker nukes. She does get stronger Resta and a bit more ATA, but they don't mean much.
In my opinion, FOmar is the most fun FO. FOmarl close second.
