The flatter radius fingerboards are better for bending. With the more curved profile, the string will touch the frets when you do a bend near the body end of the neck. This is called "fretting out". Flatter fingerboards are not as comfortable to play, so you have to pick a compromise that you can live with.

Warmoth uses a compund radius on their finger boards to offer the best of both worlds. The radius is 10" at the nut, gradually changing to 12" (I think) at the other end.