That's just sort of question made for controversy if ever I saw one. There's a big difference between ultimate and personal favorite, which a lot of people don't see the difference in.
One of the cartridges that has the most versatile range of available bullets and effectively spans the most critter territory is going to be at the top. Then there is the purpose driven angle for those who never shoot past certain ranges, which makes an alternat cartridge perfect for them, ultimate doesn't apply to someone who simply doesn't need more. Parameters would be like this:
1. inherent accuracy and what the groups look like at 300 yards
2. bullet weight and type range for different animals
3. trajectory for long range
I love a .22-250 and a Sako heavy barreled varmint was a decades favorite, the #1 favorite was a matching .243. I'd be hammering ground squirrels on levees in the delta and the wind would start pushing the .22-250 off a few inches to the side. Switching to the .243 gave me the same trajectory but way less wind drift.
I got a lot of Yotes with the .22-250, but as the shots went beyond 300 yards the drop in their tracks factor wasn't there the way it is with the .243, at some point I just switched to the .243 as it does it all and the right bullet can be used for whatever you are hunting. I've taken somewhere around 30 deer with one and never had to do any tracking, the majority dropped where they were hit with the exception of a few that were stumbling and dead but didn't know it yet.
The .243 WSSM is a whole 'nother beast, I wish I'd a had one 30 years ago. World record 1000 yard 10 shot group was just set using one at under 3 inches!
My first Coyote (and second) with this thing were 350 and 420 yd shots that would have been problematic with a .22-250 due to tricky wind, in fact the guy I was shooting with missed his at 350yds and I got it as it was running straight away from us. Jared's first words were "man I gotta get me one of them, you made that look stupidly easy".
