Thats kind of a 1990s question ("Dont the Red Hot Chili Peppers rock?!?") versus a 2010 one ("Is Coldplay the greatest band of all time?"). Because the Gregory Whitney ($350) is very much a 1990s pack. It is HUGE5,700 cubic inches in the medium sizeand designed for big, heavy loads. The Baltoro ($290) is a much trimmer pack (5 pounds, 9 ounces versus 6 pounds, 9 ounces for the Whitney), and has a relatively compact 4,300 cubic inches of capacity.
The Whitney was designed in a day when tents weighed six pounds, Gore-Tex parkas were a pound or more, and boots were five pounds a pair. Once upon a time, I would have said that was the pack to get, because only a pack such as the Whitney could handle long trips on the AT or elsewhere. But these days, the Baltoro should be plenty of pack for a trip of even five or six days or more (provided this is not the winter and you arent lugging a big load of cold-weather gear). And it's much better for weekend trips. Really, if you have a good light gear setup, it will take up only half the pack. The rest of the space can be for food and fuel.
Then again, Ospreys Aether 70 ($260) has the same room as the Baltoro, weighs pounds less, yet still has a suspension that is well up to the task of carrying gear on a long trip. You even could tryREIs new Flash 65 ($170) which is just a tad smaller than the Aether or Baltoro, yet users have found that it manages trips of up to a week.
So, my advice: Get a smaller pack and join the modern era. Big backpacking packs are just so...Dawsons Creek.