Both the at's and mt's by BFG are great all around tires. And I agree that the at's are better on the road in rain, slush and most snow.
However, I beleve that in very deep snow on the road and most snow off of the pavement, the M/t' may work better. Kind of the same way that they throw more mud out of the way. Of course, that is just my belief based on my expierence with both tires (in the 235/75/R15 size) on 2 XJ's, and a set of the m/t's on an ancient dodge van (yeah, I was called crazy for putting them on there).
But back to the topic, yes they both work well (for pretty much everything), and the A/T's do better in the snow that you will probally be driving in.
Edit: And yes they both fit just fine on both our '96 and '99 XJ's, even with sagging rear springs.