Well Uncharted looks, plays, and at least has a plot, so I'd have to go Uncharted.
I don't have a 360, but my friend brought his over for a night and I played Gears. Although I like the multiplayer options, other than co-op they all suck.
The graphics of Gears are so overrated. I remember reading game developers hyping it, and then I saw pictures.. and couldn't quite see what was amazing about it.. I figured I'd need to see it live, saw it and still.
The first time I had a couple of hours in I realized it just had no color, generic locations, story, characters, etc.
I hate how big the character models are in Gears of War and other Epic games, it's so god damn annoying and it makes moving so awkward and clumsy. It feels so awkward because you are moving through fairly tight areas with characters that are far bigger than they should be.
I nearly bought a 360 for Gears. I nearly bought into the hype, but I just held back, thank god.