I for one feel there is nothing on the market capable of reaching out past 100 yards besides the .50 BMG. Get yourself a Barret and be done with it.
oh - sorry - been reading too many gun mags.
.223 will work just fine, along with 22-250, 243, 6.5mm, etc.
It really comes down to what exactly you want to do with it. If you're only ever going to be plinking paper at the range - don't bother going up to a .30-06. It's overkill on your shoulder.
Realistically - even if you might end up getting into hunting/etc at some point - i'd still go with a lighter caliber now. Use the lighter/easier to shoot/cheaper to shoot caliber gun for getting down your technique and practicing - and if/when you decide to step up to something bigger, it's an easier transition.
Range Sessions lasting more then a handful of shots with something like a .270, .308, or .30-06 are just asking for a flinch develop. I actually just went through this myself - and made the (somewhat) mistake of picking up a .270. The idea being to get back into shooting, and hopefully next year get back into hunting - without having to buy two different rifles. As it stands right now - i'll be buying a lighter recoiling gun as soon as I can, since after about 60 rounds of the .270 across 2 range sessions, i'm already developing a flinch (luckily it's the "finger doesn't want to pull the trigger" flinch, and not the "body jerks violently" flinch).
So I guess in short - do yourself a favor and get a smaller caliber lighter recoiling rifle for range-only work. Heavier hitting hunting rifles are not something you spend hours on end shooting if you value having a working shoulder.