Technically speaking, I feel like MGS4 is better. But Uncharted is more pleasing to the eyes due to all the colour and varied environments, and that's more important to me in terms of graphics. Both games look beautiful. And when I get my PS3 back I'm gonna replay both.
Just finished Uncharted last night. I'd definitely say that it's the best looking game on the PS3 by a wide margin. I have yet to play Ratchet & Clank, though. Looking forward to giving that game a try this week.
Just started Act 2 last night of MGS4 and the opening cutscene (especially the first minute or so) dropped my jaw. I had to keep pushing up on the dpad to make sure it was realtime.
I fully admit to knowing nothing about all the technical stuff you guys mention, but from having played and beaten both Uncharted and MGS4, I can honestly say that MGS4 looked better for me.