Go to ANY luggage store or outfitters store or even Wal-mart and TRY SOME ONE.. then pick the one that is the most comfortable. I have a COLEMAN that I have had for years and it's been is well over 100 countries. It has self storing shoulder straps, a single shoulder strap and a carrying handle, so it can be configued as necessary.
The MAIN TRICK IS... when you pack it NEVER and I do me NEVER put MORE than 40 POUNDS in it.. You can easily carry around a 40 pount backpack.. but when you add any more weight than that.. it starts getting heavy in a hurry.