Well, if you have a gsr motor already, I wouldn't swap out the gsr head for a b16 head. Sure it flows a tish better at high rpms, but you will loose .2 compression and therefore loose power. Spending the money on different pistons/headgasket/ect would make the head swap pointless just to get back to gsr hp/torque.
But, if you have a b16 motor, swapping the smaller b16 block for a larger and stronger b18c block is an excellent mod, called the poor mans type r. Yes, you will still loose .2 compression and not make quite as much power as a gsr, but if you use your b16 pistons, you have relativley the same compression and be making a lot more power than a stock b16 for sure, and more importantly, gain low end/midrange torque.
As for LS/Vtec vs. Poor mans type R, the LS/Vtec will probably make more power if done right, but is a harder conversion to do. The gsr block swap is a direct bolt on.