Betsy, We're a Mac family and I'd never change. When I need a new computer I just go to the apple store and buy the newest and greatest I can afford. I never shop around.
I'm not into designing quilts on the computer however and can't help you with that question. I do know that there are many pc programs that will not work with an apple computer so investigate everything thoroughly before switching. Go to a Mac store and tell them what you want to do with your computer. They're a good group of people and will tell you up front whether you'll be happy with a mac or not. (They want you to be happy!)
Also, look at the system requirements on your software manual.