If you want to win a lot at 2v2 RT I'd play UD and just go DK+Fiend opening every game. Depending on how strong your ally is/how good your opponents are you can end games very quickly with that strategy. Problem with the other races is they lose to mass stuff, if 2 people get in your base with a ton of units you'll not be able to micro out of it as effectively. With UD you can force exchanges where you don't take any damage and can potentially win the game yourself early on, all while teching to the best late t2/early t3 army mix of DK/lich/CL + fiends+stats+orb+destroyer and not having to expose yourself to expanding early on to be strong later.