i would suggest one of the current "super-slim" ps3s, since they run cooler & quieter than the older slim or fat ps3s.
They've been steadily removing stuff like ps2 backward compatibility, ports, and linux support for a while now though. So if you want any of that you have to go with an older used one.
link showing the different specs over the years
http://en.wikipedia.org/wiki/PlayStation_3#Model_comparison
I don't think the US gets the 12GB flash version, so you're stuck with either 250GB or 500GB of storage.
The drives are user replaceable, so it doesn't matter too much what size you get. You might even want to replace the stock 5400rpm drive with a 7200rpm or SSD for snappiness (or even games that more or less stream textures in like RAGE).
Many of the games allow saving some content to the hard drive to reduce load times. I haven't filled up much of the 250gb drive (maybe 1/4th of it) I replaced in my fat ps3. I do most of my gaming on PC, but have maybe 20 or so PS3 games, mostly games that seem like a controller would help.
The ps4 might be released at the end of the year, if that matters any.