Open Sicilian Question

In positions similar to the one shown, which bishop is better for white - light or dark?

I play these positions for black, so really what I'm asking is which bishop should black try to capture - the light-squared bishop or the dark-squared one?

Is it even a good idea for black to try to capture either bishop, e.g. in this position after Ne5, Nxd3?

My understanding is that because white has a space advantage, black should try to exchange at least 1 pair of minor pieces to make it easier to maneuver his pieces.

What if instead, white had played Bf4 and Qd2 - would it then make sense for black to play Nh5 and try to win white's dark-square bishop?

Thank you for your comments and suggestions!