I'm not a really strong player but I think capturing with the b-pawn is probably better. As you mention, the adage is to capture towards the center but you also need to look at what that accomplishes in your example position, which you do.
I think it is enough that the capture helps support the center and support the push to d4, increasing central pressure. It also opens the b-file for your rook and the dark-square bishop can potentially go to b2 further supporting the center (though, I'm not saying that is absolutely the best location for the piece).
Which capture is more fruitful for White: d pawn capture or b pawn capture?
This problem has hassled me for some time now. I personally think that capture with d pawn is good for White in a long run given the fact it places the White queen in a semi open file and opens up diagonal for dark square bishop. However, wouldn't this go against the common saying, "capture towards the center?" And wouldn't a capture with b pawn ultimately support d pawn push later in the game?
Any thoughts?