Well, I'm with Bill on that question: all of them (or at least most)
However, what has been going through my mind lately is to repeat the trip I did way back in 1985, traveling alone hitchhiking and backpacking. That was the trip that really gave me my passion for backpacking <3 It is special to me because I was so young and innocent and bright-eyed at the time.
I began backpacking in Prairie Creek Redwoods State Park in California, then on to the Queen Charlotte Islands in BC, Chilkoot Trail in Alaska, Kluane Nat'l Park in the Yukon, Banff, Yellowstone, Hawn State Park in Missouri, and finally, a wonderful long trip in the Ventana Wilderness in Big Sur.
I knew so little about backpacking and my gear was so crappy! I must have had an angel on my shoulder because I was blessed with abnormally good dry weather on the trails and many wonderful people who picked me up hitchhiking for something like 7000 miles. I think I need to do this again soon (well, minus the hitchhiking, I'm kind of old for that