I'll probably buy a Mega over a Crew as long as they offer it. The 8ft bed as its advantages for sure, the 50gal tank being one.
On the Mega side, you have so much more cargo space when you fold down the rear seats. I've used it many times and it is useful to me. Also, the behind the rear seats space is great to store a lot of stuff. I have 3 medium size duffel bags in there, filled with equipment, tools, etc.
The shorter wheelbase of 1ft or so is welcomed in a parking lot. So many times I can barely make it, I can see the longer one not being able to make it. Same thing with u-turns. There is a lot of them where I can barely make it on a single turn, I can see the wider turning radius of the 8ft bed not making it. That one is not as critical as you can still make it after backing up a little. But its not as quick obviously.
And for the look... I just love it. The Mega dually is the best looking dually on the market in my opinion. Sorry long bed guys.