I very much like PPP. I only saw the last 2/3 of BPB once, back on my first DCA visit in 2007 and shortly before the end of its run. It was pretty cool from what I remember, but I didn't have the chance to become familiar enough with it to accurately compare the two.
Play Parade should be called Squirt Parade. You don't play. You get squirted. The floats and nice and all, but my twins really enjoyed the interactive nature of the Block Party Bash. And the performers were amazing!