Went through this exact debate personally for the past while (hence my choice of current rifle) - Ruger Guide Gun in .30-06.
.30-06 over .308 because it'll do EVERYTHING a .308 can, and just that little bit more. It's got a hundred years of support, and has just that little bit extra case length for seating longer bullets. Going up or down from .30-06 gets either excessive (.300WM+) or self-limiting (Opinion - the .308 is arguable for this).
Much as I LOVE the 6.5 series, they're NOT terribly cast-shooting friendly, and support for them isn't nearly as good as the .30's. I ran through a few 6.5x55's (loved them all) before getting tired of all my reloading/shooting accessories being unavailable for the caliber or out-of-stock locally for a long time.
I went the Guide Gun because:
- Mauser action - reliable and easier to keep track of brass, 3-pos safety, and hinged floorplate is more reliable than a mag that can detach and get lost. Also, CRF/Bolt-action is much more tolerant of neck-sized reloads (such as those made by the Lee Loader "hammer-time" kits) and most handloads in general.
- Laminate stock/Stainless finish - all-weather, least affected by temp changes.
- Adjustable LOP - short for winter, mid-length for summer. NICE buttpad too.
- Multiple sling-mount points. In theory, I could even do up a demi-Scout configuration using the barrel mount, stock mount and buttstock. Or, seeing as the sling mount on my fore-end is the usual Uncle-mike's style, put the bi-pod on the stock and put the sling on the barrel band.
- Express-sights from factory. Most of the open-sights shooting I'll do is sub-100yds. Worst case, the front blade is replaceable and the rear mount is compatible with the stock Ruger open-sights - so I can trade out the Express for Adjustable.
- Likewise, the rear scope mount can take a screw-on NECG Peep/Aperature sight, giving me a nice good sight-radius on the rifle. Or, since the included rings would classify as QD (as they index on multiple slots in the Ruger receiver and have knurled knobs) I could attach a 4x or 6x scope for those longer-range shots.
- Threaded muzzle - Brake came with it (easier for LR shooting in open areas), and weighted cap that tends to knock down blast. 5/8x24 threading means ANYTHING from an LR-308/AR-10 muzzle goes on mine too. Suppressors, other muzzle brakes, flash-hiders, etc.
My other options were a Marlin 336 or Win94 in .30-30 (Marlin for stainless, Win94 for more cast-friendly rifling), or an AR-15 so with "one rifle" (the lower) I could run everything from .22LR to .50 Beowulf, and it'd be LIGHT. AR-10 for .308-class capability. Or a Rem700 in .308 Win.
Declined the Levers because the .30-30 DOES eventually cap out in power - and doesn't do as well with spitzers.
AR-15 needs mags, mags=extra things to carry, and a Semi-Auto platform is intolerant to neck-sizing and fussy about charge needed to work the action. Despite cool-factor of .50 Beowulf, 6.5 Grendel, 6.8 SPC, .300 AAC or the like, none of them are as common as .270, .308, .30-30 and .30-06.
AR-10 platforms get HEAVY. Heavier than fully loaded Bolt-action platforms.
The R700 was a close second to the G/G, but I LOVE CRF (and Mausers in general), and have no use for a short-action rifle. I can work the bolt almost as fast for LA as SA, and I am not concerned about the extra powder loaded per cartridge.
Plus, I'm a NH native. I like having a weapon that's born and raised in the same state I was.