Stock for stock the VTEC head is gonna flow better, you could port the LS head though. A stock b16 head will flow a tiny bit better up top, a GSR a tiny bit better down low. But the GSR will bump up your compression ratio a little so you will gain some power there 2!

Bottom line, your gonna make more power with the VTEC head like you already stated. Are you gonna have a built bottom end? What are you gonna do about the RS ratio? You gonna throw some GSR internals in the LS block?

I guess it all depends on your budget..

Been there and done that, let me know if you have any questions..

Good luck with it!