The standard fingerboard radius is 9.5" for all current 4 string USA basses.
I've had 7.5, 9.5, and 12 inch radius G&L bass necks and I don't really feel a huge difference. My favorite is the classic #6 that was the narrow option for basses up until around 1998. They then made the 12" radius standard for basses until about 6-7 years ago, when 9.5" became standard.
I've found necks of all 3 radii that were very comfortable and some of each radius that weren't comfortable. For me, the rounding of the edges and the back contour are much more important to me than the radius in terms of how much I like a neck, at least within the 7.5-12" range.