Re: 22/6mm vs 22/243 vs ???
If you are going to use a short action, IMO, I would go with 22-243 or one of it's varients. If you're using a long action, pick whichever one tickels your fancy because they both are near the same thing. I personally like the 22-243 and it's varients a little better because you can not only use Lapua 243 brass but 243 brass in general is much easier to find.
I've got a 22-6mm on a Rem. short action. It shoots 75grainers extremely well and fast but I have to use it as a single shot because my OAL is to long to feed thru the mag.