If you're planning on never spending any money on the B16's internals, then go with your "fully built" ZC.. depending on what you call "fully built". I'm assuming that you're going to run good intake/header/exhaust with each one, right?
What you could do with the ZC:
Higher compression pistons
Custom ground camshafts (if you can find someone to do it)
Adjustable cam gears
Port & polish
And of course the support pieces that you would need for this...
Compared to a completely stock B16, this setup tuned properly would probably outrun it, not to mention be lighter... but it would also cost more. Then again, you still have to tell us what you mean by "fully built".
Honestly- I would go with the B16, since there's so much more you can do with one... the aftermarket is plentiful for this engine, and it's just a more solid platform to build on, compared to the ZC.