IMHO, if you want to move virgin dirt around, a rear blade (heavy one) is the way to go. I can back up, drop the blade and just start rolling soil/sod/whatever up with my rear blade. I can cut ditches with it, pulling 12" deep in one pass in a lot of places. It's a "dirt cutting" tool. My box blade is a "dirt moving" tool. Yes, I can cut with the BB too, but it's much, much slower than the rear blade. There's an EA video out there where Ted and Peanut are using a BIG box blade (like 1 ton blade) with a huge tractor and ripping down to soil. It does the job, but it takes a lot of passes to pull the sod off, and it's not moving dirt from point A to B, it's picking up dirt and leveling it.
I do a lot of trail maintenance, any my typical order is 1 pass on either side of the trail with the rear blade angled and tilted, cutting a big ditch and pulling all the spoil onto the trail. Then, after that, I'll hook up the BB and smooth all the ripped up soil back down into a nice trail. I'll generally make a few passes with the BB to do this, tilting it further and further back each time (so that it rides more and more on the rear blade and picks up less material) to get a nice smooth surface. If I'm showing off, I'll then pull a chain drag over it to get it really nice, but the rear blade + BB gets me a ditched and smooth trail.
I could do it all with the rear blade. I really think that a big rear blade is the more "do everything" attachment in this class (especially if it is has tilt/angle/offset adjustment and even more so if you have shoes and end plates). It can do whatever a box blade can (well, except for cutting in reverse), but it's not nearly as good as the BB in certain tasks. The BB is much better at some things (smoothing, distributing gravel) and can do a lot of what the rear blade can do (generally slower). So it all depends, in my case, I knew I needed more ditching and less smoothing, so I spent more money on the rear blade and have a good, but relatively inexpensive BB. I'm happy with the mix for me, but if I was moving crush and run all day, that wouldn't be the right way to go.
Others have already said it, but WEIGHT! And, if you wind up with the rear blade, I'd add "hydro adjustment!" to the must have list. My blade would be much less useful if I didn't have tilt/angle adjustments from the seat, yes, I could still do it, but I wouldn't, it would be too much of a PITA to cut down miles of trail and adjust the blade every time the slope/angles changed.
Here's a video of me rolling up a trail with the rear blade:
Bison NB8-24 More Ditching - YouTube
Bison NB8 -24 Pulling a ditch in hard clay - YouTube
And then, after that, I'd run the BB down it to take the hump out and lay everything down nice and flat.