ITA with your decision. The WB is wonderful for our 2 boys' stuff plus my stuff when we go swimming. But even on a double stroller, I wouldn't really want to carry it all day. But the brb is wonderful on the back of a stroller or worn. And I love the zippered sippy pockets for your water bottles. It would def hold what you need it to, except the towels. And the towels would fit in the MB no prob.
What colors/patterns did you get?