I dunno. Tough call. I lean toward the .243 win. Don't kid yourself - with 55 grainers, .243 will push 4200+ fps screamers out that match or exceed .22-250 velocities. This with, oddly enough, better BCs, IIRC. So the .243 is definitely a superior ballistic round for *very very long* shots and/or in *high wind*. But if all your shots are 300 yards or less, it doesn't matter, in which case the .22-250 will work fine/great. Yes it uses lower BC bullets that bleed energy much quicker, but they're going so fast that this doesn't matter until past 300 or more yards. So then you can use .22-250 which as mentioned has the advantages of (a) cheap WWB factory ammo, and (b) less recoil, and (c) someone said handloads are less finicky to find good ones - I don't know this myself to be true, but I can't argue with the man's experience, so let's chalk that up as an advantage also. Flip a coin. Really, the bottom line is probably this:
-If your "varmint" is a coyote, AND you might take 300+ yard shots in the wind, then go with .243.
-OTOH, if your varmint is P-dogs and such -- OR - if your varmint is p-dogs plus yotes, but you won't be taking any super long shots, then .22-250 is superior.
We threw 6mm Rem into the mix above. Can anyone compare .22-250 and .204 ruger? 'Bout the same abuse to your barrel?