My preference is a pack with a capacity of around 4200-4500 cu. in., designed to present a rounded profile when loaded, but with the ability to accept attachments.

Overloaded packs do not fare well in heavy brush, but there are times when you must hang stuff on, at least temporarily. An example would be going on a climb - starting out carrying your rope on the outside. When returning and provisions have been consumed, everything goes inside.

There are plenty of pack designs that incorporate a smaller day pack into a large heavy hauler, usually giving you the best combination.