Bags are very personal things, but I'm fond of backpacks, in particular I like the fact that I don't have to remove my laptop when going through security. Holds my laptop, my iPad, my iPhone in phone pocket, bottled drinks on the side and plenty of room to spare. 120k miles on it over last year and looks brand new.
My most useful bag (when I'm checking a bag). Drop bottom duffel allows place to put shoes, dirty clothes, etc. that I want separate from main compartment. Hard to go wrong with Victorinox, when they say lifetime guarantee they mean it and it's no hassles or receipts