Here's the cold hard truth...there's no such thing as a comfortable pack. I would personally look at packs that are the lightest, with the most padding in the shoulders and most support/padding on the waist strap. You want a pack that puts the majority of the weight on the hips and not the shoulders/upper back. I like the eberlestock gunslinger II, but I also know there are more comfortable packs out there.
Even though I'm a Mystery Ranch/Dana Design die hard user, I completely agree with 300, once you get north of 65 lbs. none of them are comfortable IMHO! I think some of them just carry the weight better & might not feel as bad. But I've never had a comfortable pack on with a lot of weight.