Sorry, I'm going to have to correct you.
The ZC that most people swap in produces more power than the SOHC VTEC engines because of a few simple things... more aggressive fuel mapping (although almost nobody runs the original ECU), TWO camshafts, and a different head setup. All the other D blocks are single cams (except the 86-89 Integra).
The SOHC VTEC engines have considerably MORE aftermarket support than the DOHC ZC. They're more popular, they actually came standard in the States, and they're newer. It's very difficult to find DOHC ZC upgrade parts.
The DOHC ZC is a great engine to swap into your CRX or 4G hatch, but you won't be able to do too much to it unless you want to custom make your own pistons, rods, cams, etc. Most people strap on a turbo and call it a day. It's the easiest and really the only economical way to get additional power out of a DOHC ZC block. Now the SOHC VTEC engine on the other hand... you can put DOHC ZC pistons in it to raise your compression, choose from any number of aftermarket camshafts, even buy a Skunk2 or Edelbrock intake manifold for it etc.... there's tons of stuff out there for it. The SOHC VTEC engines are also newer than the DOHC ZC, so chances are that you'll find one in better shape.
If you want to just swap in an engine and call it quits, the DOHC ZC is probably the way to go. If you want to upgrade step by step, the SOHC VTEC is your choice.