The best way to distinguish the different models is to become familier with what three engines look like. When you're looking at a car, you can pop the hood and instantly know what model it is.(Unless the owner swapped the engine) You'll prolly have some trouble finding a decent one with 4ws.

The three engines are very different in appearence. The 135hp F22 is SOHC, the 160hp H23 is DOHC, and the H22(vtec) is DOHC and says VTEC right on the valve cover.