I'm new to snowboarding, but the guy at the shop tells me that the two companies have different fits. Chances are you'll like one and not the other. With that said, I purchased the Rampant boots and right out of the store, I felt they were a little too snug. I felt some excess pressure on the sides and heel. I wanted to move up to a 9 from an 8.5, but he said it should be fine after a day of use, as long as I didn't fell a burning sensation and my toes didn't curl.
Needless to say, he was spot on and after the first day of about ~8hrs boarding, the boot felt like a glove.