I have never played any of the hacks really, just seen a bunch of videos. And I have to say, Project M looks like a HECK lot more fun than Brawl plays. I know, two totally different functions being compared is so whack, but let me explain.
When I first saw vids of Brawl, they looked otherworldly. I couldn't wait to get my hands on it. This was back in, like 2006 as I recall. Seven years later when I actually get the game, I find it's floaty and slow (facts I knew well before I got the game btw). Competitive play is a LOT slower than Melee's was, and seems like you have to do less in order to get good. Characters in Brawl are so much NOT viable for competitive play, whereas in Melee you could very well find a serious Link player who could win against a great Fox/Marth (e.g...what was his name, IZAW?).
Project M brings the fast paced, highly technical gameplay back or so it appears. I'm most looking forward to wavedashing; I don't care if it was a glitch, it made Melee 100x more enjoyable for me. To see it go away for Brawl really pissed me off :I