Round ones are good.
I heard square ones aren't in style anymore.
Style has something to do with it? Darn!
Well, I run a lot of rock - Slickrock, whenever I can, and the rocky/sandy trails of the Rocky Mountains the rest of the time. I DO like my MTR's, except when I hit slushy snow (I'm talking about on paved roads) - they don't do that good. I have a friend with 35's under her TJ, and she's got them siped, and seems to work pretty well. When I asked the Goodyear guy about siping, his eyes got kinda big, like I had just suggested performing lewd acts with his little sister, and said "NO, you do NOT want to sipe them!"