Well, if you're getting one for cheap, then the PS3 is not a bad investment at all. You'll have a huge library of games to play around with. The Playstaiton 4 and the Xbox One would take some time to settle in with their respective titles, so it would be a while before that happens. Besides, the games would be quite expensive. Most of the PS3 exclusives now can be obtained for nearly half their launch prices, or even less. There is no assurance that any of these game would really cross-over to Playstation 4. If you're ready to let that go, then you can wait and go for the PS4.
I bought the PS2 when it was almost towards the end of it's life-cycle and the PS3 was quite a rage. I never regretted it's purchase, for the time that I've had it. Suffice to say, you wouldn't be disappointed with the PS3 either. Coming from a PC gamer, visually, you'll be quite disappointed. These are aging consoles, so it won't be able to match the crisp visuals quality and performance of a PC game. However, there are some titles which would really make leave you flabbergasted with their astounding visuals.
If you already have a PC and a 50 inch Television AND use a 360 controller, I'm not sure why you're still using your PC monitor for gaming. You can use a 360 controller with a PS3 via a 3rd party adapter, however, you loose the motion sensing ability with it. This support is not confirmed on PS4, as it hasn't even released yet. You'll just have to get used to the DS3, which isn't difficult. The only problem area with the DS3 controller, for me, were the shoddy triggers.