Since your original question is between the Mega (SB) and the crew (LB), you're not talking about a difference in wheelbase or turning radius -- thus driving the truck (and parking it) are the same either way.
That said, I've had exactly one truck in my life with less than an 8' bed, and I cussed it nearly every time I used the truck to haul something. It was a 1/2 ton, so I never considered towing anything from the bed (5th wheel or goose-neck) -- but I wouldn't want to do it regularly in a shortbed truck.
But that's just me, and my experience started when short-bed trucks weren't the norm -- there are PLENTY of goose-neck and 5th wheel setups that accommodate a short-bed truck just fine. it's just not my preference.
So for my money, it comes down to how you intend to use the truck. If most of your hauling will be loads in the bed, and trailering from the bumper, the Mega cab is a fine option, especially with kids and/or pets...and more covered cargo space in the back of the cab.
If you're going to haul a 5th wheel or goose-neck regularly, and/or plan a toolbox (or auxiliary fuel tank) the 8' bed is really really nice, and a crew cab is lots of room too!
One thing is for sure: If you're on the fence, odds are pretty good that either decision will work out fine. If you HAVE to have either the Mega or the long-bed, you'd know that for sure. You'll be able to work around any other limitations you encounter.
I'll qualify all this by saying this though: I'm so married to an 8' bed after my experience with a short bed that the only reason I didn't seriously consider an ecodiesel 1500 for my needs is that I couldn't get it with an 8' bed. I've had my last shortbed truck....so I MAY be just a WEE bit jaded, and you might consider taking my advice with a grain (or block) of salt.
