I prefer and recommend the 308 Win. But like anything else that involves comparing two firearms, two types of powder, or two different calibers everyone has their own opinion. I live in Kansas and do a lot of whitetail hunting. Most shooting is between 50 and 400 yards. There are some longer shots availible at times, but climate conditions and the experience of most hunters in my area make these types of shots very difficult.
Most of the guys where I live swear that you cannot kill a whitetail with anything less than a 7mm or a 300 Win. To me, shot placement, not caliber, is the name of the game. If you hit the animal in the vital area, then you will harvest it, end of story.
If you are planning to reload, consider that the 308 round uses 38-40's grains of powder, while the 7mm uses 70+ grains. Something to consider if you want your reloading dollar to go further.
The 7mm is an accurate cartridge, don't get me wrong, but I think that you need to carefully consider the application that you will be using the rifle for. It's been a while since I've been behind a 7mm Mag, but the recoil is somewhat greater than the 308. This isn't something you may notice in a few shots, but if you are planning to use this rifle as a long range varmint rig, then the recoil may take its toll on you.