You could always do a combo of round and square. My neighbor has a round bed in the front corner of her house and I guess it's more of a rectangle bed along the front of the house. Then on the other front corner she has another rounded bed.
You do whatever you like. I personally like flower beds that are oval. They just look better to me. It's a personal preference. You could do some round and some square. How many are you putting in?
I am thinking at least 2 good sized ones at the front of the house and maybe a few small ones on the perimeter. I want a good mix of flowers and shrubs.