I haven't worn shorts in about three years, but I'm currently in the market. I will primarily wear capris and maybe a few skirts but I'm going to WDW in August and I've recently lost a couple of pounds so I'm treating myself. However, I went to two stores yesterday and all the shorts were soooo short! I was horrified. Who at my size (or any size) would want a one inch inseam?!
Anyway, I've found that well constructed shorts made from heavier fabrics like denim are much better than any other fabric. Shorts with cuffs also "weight" the fabric down, although they visually *cut* the leg in half. Try on shorts and walk around for 30 seconds. If they migrate, DO NOT BUY THEM. Also make sure that they are long enough. In addition, if they are too large, they will also roll up more easily. They should fit comfortably but not tight or too loose.
I was in WDW last year and I saw a more than Pooh sized woman in a large tank top and what appeared to be nothing else. Only after a few glances did I realize she had on shorts that had rolled all the way up and only two pink flaps on her outer thighs were visible. It looked uncomfortable and embarrassing.
I also have to share - I wore a skirt and tank top to work last month with sandals. It was the first time I can remember in quite some time that I did that. I came home and sat down and realized- I wasn't chafed at all. It was a proud moment (yet slightly embarrassing to retell on the DIS

) I was surprised when I realized it, though! So, I've been wearing more skirts since then.