My first suggestion is not to limit yourself to factory ammo. Handloading can be started with a very modest outfit, with an initial outlay as low as $250 for a light duty press, dies, shell holder, scale, and a loading manual. Handloading will allow you to shoot more for each dollar spent on ammo, and you can produce better, more accurate ammo, made specifically for your rifle, than you can purchase.
Older rifles with 1:14 twists are close to their limit with 55 gr lead core boat-tail bullets, but the 1:14s are seldom encountered anymore except in older guns, or custom barrels. Typical .223 chambered varmint rifles, like my CZ 527 full stock comes with a 1:12 twist which will work with all bullets up to the length of the Sierra 63 gr semi-spitzer or the Speer 70 gr RN bullet, so its not a bad choice. Lighter bullets, that due to their construction, and/or design are longer, will not stabilize in a 1:12; neither of course will heavier-longer bullets.
My preference is for the fastest twist I can find, which in a .22 centerfire seems to be 1:7, although factory barrels can also be found in 1:8 and 1:9. A fast twist has no disadvantage with respect to accuracy, over stabilization is a myth in my opinion, but it has the advantage of handling any longer bullets which might be encountered (with the exception of a couple of VLDs that require 1:6.5) and terminal performance is enhanced when a bullet is fired from a fast twist barrel. Fast expanding varmint bullets are more explosive, due to the high rotational velocity, and game bullets penetrate deeper, due to the fact that they come out of precession (yaw) faster. One small downside of the fast twist barrels is that thin skinned bullets designed to expand at .22 Hornet can, and do, explode in the air before they'll reach a 100 yard target, but loaded with bullets designed to function at .223 and .22-250 velocities perform just fine.
If your shooting was confined to the flat base Speer 50 gr TNT, the 1:12 would be fine, as with most lead core 55 gr bullets, but if say you wanted to shoot a Barnes .224 55 gr MPG, you'll need a minimum of 1:9, and a TSX game bullet heavier than 53 grs will need a faster twist than 1:12.
