I would recommend a PS3, the fact that it's fairly easy to jailbreak at this point makes it one of the best. There's also tons of emulators for it that you can play games from other consoles with.

If you're hoping to only play legitimate software it's still a pretty good choice given most charity shops have a good supply of games, blurays also don't scratch as easily as regular DVDs.

A lot of consoles older than the PS3 esp anything from Nintendo GameCube and previous are in huge demand with collectors so you'll be paying a ton for some of the more desirable games.