If your smart you would grab a traditional Gen 3 Glock. The new Gen 4's don't really offer any great improvements over the Gen 3 and some have reported problems.
As far as the "C" model goes is this going to be a carry gun, range gun, or both? If you are going to carry it you will have to take into consideration that shooting in a no-light or low-light situation it may temp. blind you making follow up shots harder.
While I don't own any RTF models I have held and shot them. I personally am not a huge fan of the RTF. For me they are too abrasive compaired to the stock grip finish which to me does its job just fine.
So my recommendation would be a stock Gen 3 G23