If it is an option, B18C(GS-R), no question. It displaces more. Both can take a low boost turbo without modifications, however it would be a very good idea to give them low compression pistons before you think about a turbo.

The B18C (GS-R) also comes with a funky variable intake manifold that you should probably ditch before installing. A Skunk2 manifold would be the replacement of choice.