It just depends. All three are awesome rounds in their own right. The 300 WSM will be the easiest to find ammo for. You can not go wrong with any of them.
I too have A-Bolts, 3 of them to be precise, but no experience with the X-Bolt. That is the reason that I asked the question. Thank you for the useful replies so far.
I looked at a Browning X-Bolt tonight. I really liked the feel of it. Light, maneuverable, and in the caliber that I am looking for. My question is about the polymer rotary magazine. It looked and felt really cheesy. Does anyone have experience with these? Do they hold up?