Since I'm assuming you're a girl, this is definitely a purchase you want to do some in person shopping for. I recently got a Mikita variable speed 5" random orbit sander to sand some cabinetry I'm building and am really happy with it.
I was all set to buy another (slightly - a couple dollars at most) cheaper one on Amazon, but checked them out at Home Depot at the last minute. So glad I did. Most of the brands were too big to comfortably grip in my small-ish girly hands for long periods of time. The one I selected has multiple places you can grip - including an attachment you can take on and off to enable holding it with two hands.
TL/DR - unless you have hands the size of an average construction worker, definitely look at these in person before buying.