Always, always carry on. I travel a lot, sometimes weeks at a time, and I've learned to travel with a roll-on and a medium sized Chanel duffel. I put my purse in the duffel when I carry on so it counts as my personal bag. This has always worked, even when I went to Asia for two weeks. Thank goodness I did that, because even though I planned on checking in, the check in representative told me I shouldn't because of the short layover I had in SF - she recommended carrying on so I wouldn't lose my luggage.
I think the biggest problem while traveling is overpacking. I make sure to coordinate my clothes before I pack so I don't overpack. Last week when I went to Miami, I packed 4 jeans, 1 dress, 2 sneakers, 2 shoes, 3 skirts, 2 capris, 8 tops, 1 swimsuit, various belts, jewelry bag, makeup bag, liquid bag and intimates between the two bags. I had plenty of outfits to choose from while I was down there, with some shirts to spare.