Both. I already have the same mounts as you at both ends, but with single Bilstein 5100's at each corner now. My Bronco is light in the rear, but heavy in the front with the Hanson and winch. And I can feel it.
The rear rides perfectly in my opinion (a little stiff perhaps, with the quite old WH springs, but not as bad as stock), with good control and decent ride. But the front is a tad bit soft, which was half expected with my setup.
With the Detroit Locker in the rear and the slow steering (stock rebuilt 6-turn box) I wouldn't mind firming it up a little bit overall.
Going duals in the front is an obvious option, while duals in the rear is just for fun. Because I can, and like to play around.
And also it doesn't hurt to have more personal experiences so I know what I'm talking about sometimes.
For which mount to utilize, in the rear it makes no difference because they are angled the same and use the same length shock. But the behind-the-axle mount is the stock original on these, so is the one most often chosen. Some exceptions might be if you have one of the rear disc brake kits that requires relocating the lower rear shock mount. In that case you would just choose the front mount and leave the old mount where it is, unused.
Another option is to go with opposite ends on either side. The theory is that this mounting strategy helps reduce axle-wrap and is what some manufacturers did from the factory. GM did it on their '73 to '87 trucks.
Otherwise, it's just user choice.
On the front, I could actually try another single setup, where I remove the shock to the rear of the spring (stock location) and install one on the front mount. This serves two purposes. I can opt for a shock with stiffer valving right out of the box and try that by itself, or to my way of thinking, a shock mounted forward of the loaded point and farther away from the fulcrum has more dampening effect. I don't know how much this is true, but intuitively it seems right.
Or just add a second lightly valved shock to help firm things up and run duals.
Just like you, too many choices!
I once had aspirations to check every RS9000 shock of different part number, but of the same size on the same mounts (approx. 10 part numbers), to see if one was better than the other for a Bronco. I loved the adjustability, but really was disappointed with the overall ride quality of the standard one and just thought it could be better. And knowing that there were four part numbers (now down to two I believe?) that were valved specifically for use as dual shocks, I really wanted to try those out.
Because Rancho does not specify the valving differences between part numbers (if any) I thought since I'm in the industry I might as well be the test dummy and let others know what I find out. Like I did with headlights about 25 years ago.
Unfortunately that's still just too expensive of a proposition to do just for the heck of it, so it never happened. Yet!
Of the shocks I've personally used on Broncos (that are still on the market) the RS9000's are still my second favorite. With the Bilstein 5100's being the first/top/numero-uno for me.
But the best riding/handling Bronco I ever spent much time in was a '72 Explorer that my buddy bought and put dual front shocks on. A crazier combination you'd never find, but the rear-mount shock was a Monroe Load-Leveler (coil-on-shock overload) and the front-mount was a Gabriel Adjsutable-E set on full soft.
Man, that thing could handle the bumps and not get bent out of shape. And it rode pretty great on the road as well.
But hey, I was also just 19 and used to stiff riding old trucks too, so what'd I know anyway?;D%)
Paul