To the OP, I had a PLY for a year until the tail snapped. DC warrantied it and sent me a MEGA this year so i'll give you a lowdown of what I think.
The PLY is more forgiving than the MEGA, less stiff, but still not as playful as a rocker board. Was stable at high speeds, really good to ollie with, and was very easy to jump/land with. The only negative I noticed was the edges had alot of little fractures from hitting rails, I don't remember my other boards fracturing as much.
The MEGA feels a lot more stiff than the PLY, the first day I rode it I wanted to return it because I thought I would never get used to the stiffness. Now I'm totally comfortable on it and actually prefer it over the PLY. It feels identical to the PLY honestly except that it is stiffer so my ollies might be a little bigger. Really good for jumping, and haven't noticed my edges cracking at all.
Both are great park boards, and I think the MEGA is a great all mountain board too. And for what its worth I do about 50/50 park and trail riding.