Favorite faction is the Imperial Guard in DOW2:R, too bad they have been nerfed hard recently, they are probably the hardest faction to play.
Eldar are incredibly OP against them too.
I prefer to play as the SM, their faction seems to be the most well designed balance wise while all the other factions have balance problems.
Captain hero
Use the incredibly fast scout marines to aggressively capture resource points, hold them with hero and kiting scouts and lower tier marines
Begin to spawn a solid force of assault marines in tech tier 2, they are a little bit OP from what I have seen, but every faction has it's OP squad and these guys are jet-pack melee so they can clobber any other non-melee centered squad.
tier 3, build a MB tank and equip it for anti-armor and protect it with assault marines, this will create a good defensive force to hold CP points against armor and infantry (attack armor with the tank and jump pack marines, protect tank against anit-armor infantry with jet pack blitz)
If you guys want to play with or against me sometime, my steam name is Fuzzy Missile