Depends...

Lighest model (great for swaps but lacks in options) = 88-89 HF
Not the easiest to mod, because the hubs and axles are weak and will need to be swapped out for a B series...

The model with the most going for it is the 90-91 Si... They have the few 'luxury' options that the U.S. CRXs ever came with... But they tend to be heavier than the rest... But not by much...