Of those two, I'd get the .204. running the numbers in the program I have, the .204 shoots flatter than anything short of a 40 grain bullet @4600fps in a WSSM. That's as flat as it gets.......
More important than flatness, though, is wind drift, you can adjust the scope for flatness, but wind drift is the real bear biting you in the butt. The little .204 is pretty good here, too. What's more, the minorleague recoil lets you see where the bullet hits, and correct for it, that's a lot harder to do, with a .22/250, since the recoil is usually too much to allow for that.
The .22/250 WILL hit a lot harder, at any distance, since you're throwing a heavier bullet almost as fast, simple physics, there, but it's harder on the barrel, and kicks more. Get the .204, in other words. Ammo cost is the same, if you don't handload, so that is a wash.