I would say it's a tossup. Brady has a team with more talent both offensively and defensively. He has more reliable players around him and is going to throw less picks and probably more touchdowns. Romo has an explosive offense too, but if their defense tends to leave opposing offenses on the field longer; however, Dalas has a little easier schedule to go.
They are both incredible fantasy players and you win with either of them. I wouldn't throw in anyone extra in the trade.