I'd go for 2 backhands.
Why ? A player with 2 forehands is very limited. No slices, or at least no effective ones. Stops would be harder to disguise. Volleys are better on the backhand side for most players.
With 2 Backhands you got all these shots from both sides, of course the forehand has more potential on developing spin and speed but that doesn't make up for the lack of possibilities to structure your game. If your opponent has got a good day I want to see you trying to break his rythm with 2 forehands.
The more complete you are as a player, the more successful you will be. IMO the right choice would be , as TennisCJC said, to develop a forehand and a backhand. It is just the best of both worlds combined - 2backhands or 2forehands will always limit your play to a bigger extent than it will give you benefits.