Go for a decent PC
Since I bought my new graphic card (Nvidia) MSI N560GTX-TI Twin Frozr-II 2 weeks ago, I haven't touched my PS3 again... Batman Arkham City looks/plays really great on 1920X1080@50FPS on my TV
Looking at what happens with the latest games on PS3 (memory problems, slow etc.) I decided my PS3 is outdated now because of this. No need to invest more money in this once great piece of hardware..
Steam is garbage compared to PSN/SEN, but at least I can access Steam without the need to update Windows or the PC's Bios again and again