I've ran:
29"x dunno - lame street tires
31"x10.5", (all year - Cooper Discovery something lame)
33"x10.5", (all year - BFG T/A KO2)
now
33"x12.5", (winter - Duratrac)
35x12.5" (summer - Cooper Discovery STT Pro)
Honestly, I think the difference between 10.5" and 12.5" is somewhat like the difference between the popular Goodyear Duratrac vs BFGoodridge KO2: you can't go wrong either way.
Everyone seems to have their personal opinion on it...and I personally think they all can have some valid points. I cannot tell you the "best" answer, because that will be debated until the end of time. But I can tell you that whatever you choose, you won't have chosen the "wrong" answer.
Personally, I prefer the look of the 12.5" tires.
I also, albeit I'm in the minority - depending on where you live - I prefer wider tires in snow as well. We see about 6 months of snow where I live, so this is an important to me.
Several people will tell you that narrower tires are better in winter than wider tires.
Worst case scenario for me is that they are actually correct.
But even if that is the case, it's apparently not a significant enough difference, to me, to even notice it in 6 months of winter x 22+ years.
(I'm not here to argue wide vs narrow in snow - I'm just saying that I have a good amount of experience with both...and really do not think it makes that much of a difference, regardless of which side you're on.)
Largest noticeable difference in traction in winter to me has been tread and tire compound. Dedicated winter tires (like the ones cars get..and we don't in our size for some reason) are exponentially better in winter over all season, and summer tires. (I consider my Duratracs to be all-season. I'd still prefer a dedicated winter-only tire 35" tall. I'd take any width that fit if I could get that)
Tire height is also very noticeable with regards to acceleration, handling and weight when installing.
I will say that during the summer, narrower tires are easier to turn/handle on the highway than wider tires, and probably a lot easier on the ball joints/steering system. Cosmetics play a much larger factor for me in summer (I just like the wider look vs pizza cutter), as well as the mud and rock performance.