Heres a chart that shows all the models of the ps3 and which ones are cfw-able.
The best PS3 you can possibly buy is the CECHAxx which has the most features and can play the most games.

Use this list when assesing your PS3 or purchasing a used one.

[WARNING] When purchasing fat PS3's off craigslist or on the internet make sure they still have their warranty seal.
(It's protecting the screw on the side of the ps3 with the HDD cover)
If it doesn't it means it has probably been modified internally (usually reflow due to hardware failure RLOD)
Which means it will probably break down in two or three weeks of use.