It's personal choice, really. Also, part of the reason I joined this is I am on the fence about it myself.
I've owned 3 6.5x55's, and one 7-08. Here's my take -
For shooting - my 7-08 was in a Steyr Scout rifle at 7.1lbs w/scope and sling - and I found the recoil to be pretty sharp. I eventually added a Steyr recoil pad - and this made it MUCH more shootable, but it still liked to jump. Likewise, the muzzle blast was enough to kick up leaves out to 20' in front of me. 19"bbl, ~39.5" OAL, IIRC. The Ruger No 1. in 6.5x55 that I had sported a 22" bbl with a ~38.5" OAL, and had SIGNIFICANTLY less blast. Granted, it was still a noticeable poof, but the Scout I wouldn't dare shoot without hearing protection. The 6.5 I'd consider. The effect on bottles, however, was identical between the two. Also, the kick on the 6.5x55 was a good deal softer, even with 140gr rounds.
Downrange, in all honesty, it's neck-and-neck for ballistics, but the 7-08 hits harder, and the 6.5x55 would sink deeper, in theory. I've looked across the board on BC's of 7-08 and 6.5x55, and they do come even - if anything, the 7's get a SLIGHT edge in Berger's, but you need to be at the heaviest bullets to get this.
As far as reloading - I have been an AVID 6.5 fan, but I'm getting irritated with the market for it. It's one of few calibers that still has bullets on the shelf during the ammo-frenzy, but when it comes to accessories, you can find 7mm and .30 stuff before finding 6.5 if looking in your local store. Even online I'm running out of places to get 6.5 things. Most of the good items are out of stock for the next 3 months at least, and since 6.5 is a niche cal most producers aren't making a priority of production for it.
Also, as I'm just finding out, 6.5x55 is a very fussy caliber to shoot cast with.
Factory ammo - the 7-08 has a larger variety in the U.S., no question. However, most 7-08 factory ammo runs at 140gr, with a few going to 154 and 162/168gr. I think only the custom makers (DoubleTap/CorBon) have produced a 175gr 7-08. For the 6.5x55 - Prvi is cheaper, yes, but nearly EVERY other possible brand of 6.5x55 is going to be at least as expensive as 7-08.
Another point about the 6.5x55 - and something I hope the hunters will chime in on - I've read on a ballistic/LR Hunting website (
Terminal Ballistics Research) that the 6.5x55 has a penchant for NOT opening up on impact due to it's narrow build, and the owner of said website has had issues in the past with game getting away from a pinhole in and out. This is a much less common occurence with 7-08, from what I understand. However, the owner of the website also STARTED with 6.5x55, IIRC, and even states that he has a slight distaste for the caliber. I've heard most other actual users of the caliber having no such problems.
I've also read that 6.5x55 has a shorter barrel life, since it uses longer-burning and magnum powders, and that its long bullets with fast twists impart more ersion on the barrel lands. 7-08 on the other hand is like a "Lite 308" - and apparently has much better brass life and potentially barrel life. Again, I'd love for someone to chime in on this.
In short, if you're hunting - take either. If blasting/plinking and *some* hunting, I'd go 7-08 for barrel life and case life, as well as easier access to supplies. If target/LR Match, I'd pick either, but 6.5x55 seems to have quite the following.