As you can see from my signature, I have two A Bolts and one X Bolt. While I am a big fan of them both, I think the X Bolt wins me over. I thought the A Bolt had the nicest trigger on a factory rifle I had ever felt, until the X Bolt. The X Bolt's trigger is just pure awesome. Like someone mentioned, the magazine is made of polymer, well who cares? It is strong and it won't rust. We are so advanced in our polymer technology now I would not worry about it at all. It is actually a rotary magazine too, I didn't realize that until I had bought it. Nothing wrong with that, I just hadn't seen a rotary magazine on a high power rifle before, I am sure they are out there, I just haven't owned one until now. Another small interesting tid bit about the X Bolt, it uses a two piece scope mount base and it actually has four screws to hold on each part while the A Bolts only have two screws per piece. I also like the feel of the new Inflex, or whatever it is, recoil pad. The ability to press the bolt release and open the bolt while the safety is on is a real nice safety feature too, specially for young or new shooters. The stock on the X Bolt seems to fit me real nice too, it still maintains that palm swell from the A Bolt I like so much. As far as accuracy goes, they both shoot really good and I don't see much difference there other than I find it easier to shoot good groups on the X Bolt due to the smoother trigger it has.
I hope this helps, you can't go wrong with either of the rifles, that you can't argue with.