Well first of all I would base my decision on the twist rate. They are both proven to be excellent shooters. My x-bolt shoots under a 1/4 inch 3 shot group @ 100 yards. Regardless the browning has a 1 in 12" twist rate which is best suited for stabilizing bullets up to 60gr. The tikka has a 1 in 8" twist that can stabilize the heavier bullets with more B.C. such as the 75 gr. a-max or 80gr Bergers. Even though I love my browning, I wish it had a faster twist rate so I could shoot the heavier bullets @ farther distances.
With that being said, the x-bolt's magazine does not stick out from the stock. That's a nice feature. Also all of the x-bolts are glass bedded from the factory.
Have fun making your decision.
Just for bragging rights, here is my grouping from the x-bolt varmint.
