Not sure about any 'factions', considering when I played, it just asked which character I wanted to try, unless that's what you mean.
I'd say try any character, and if you want another character, just play the game and collect the items necessary for building a new character.
Ah! I just realized we're talking about different games! The one I was thinking of is called WarMachine, it's got different armies and half of them are adorable monster men.
Link
GoatBoy
Oh! My game shop has a bunch of starter boxes of WarFrame, I just can't decide which faction to play.