Good question. If this is for a range gun, it doesn't really matter. Get what you like best, and what you can afford. But if its for a carry gun, you probably want one with a decocker. Here are the options, and they're all good guns.
CZ 75 Compact: steel frame, 32oz, on the heavy side for a CCW.
CZ P-01: Aluminum frame, 28 oz.
CZ 75 PCR: Aluminum frame, 27 oz. Very popular CCW option.
P-07: Polymer frame, 27 oz.
I prefer the P-07 for multiple reasons: 1) simpler, more modern action. 2) replaceable steel inserts in polymer frame should in theory be more durable than an aluminum frame. 3) ergonomically superior IMO, 4) better action out-of-the-box (but requires break-in and lube job to achieve), 5) uses relatively inexpensive P-10c mags. 6) less expensive.
However, @
cheby carries a P-01 with a CZC action job and it's really nice. Also, for no good reason I have a hard-on for the subcompact Rami.
If the used gun has had any gunsmithing done on it, I would avoid it. People do some seriously retarded things to CZs to try to make the action "better".
Hope this helps.