Scoobes on 31 December 2010
I prefer Steam!
Seriously though, out of the two options, I'll go for the free one (PSN). I refuse to pay for something when I get the same level of service from an alternative provider be it Steam or PSN. I've been gaming online on PC for years and the closed network of X-box Live feels too... closed. The stuff I tried with the Silver membership is nice, the demos download fast, and the interface is easy to navigate and the friends system is good, but at its core, I get more value from PSN as I still get to play online for free.
With Sony's policy of being open to third party software (e.g. Steamworks) and allowing more dev freedom (for MMOs and updates) I see more room to improve PSN as well.
