I like whoopies for the quick adjustment at the park. I like the strap & buckle system that WBBB uses just as much. Either way, you're going to need some long straps for some of the trees around here.
When I first took my kids to the park, I had to double up on my straps to get around one tree. They also got covered in pitch. I ordered a few 16' to 20' from Arrowhead and now I carry one long one and one short one (short being 12'), which gets me by.