I've got both a BD-36 and a BL-36. Both of them came with wheels that were so far out of round that I considered them unusable. I spent about 2 hours each truing up the wheels. Both of the battery chargers were defective, one just out of the box, one after a month of use. They're supposed to be supplying warranty replacements, but haven't seen them yet. The WE motors seem strong and have so far been reliable. My brushed motor has about 500 miles on it with no problem. The brushless one is less than 100 miles.
I've not seen the Ampedbike kit, but from what I've read and can determine by information online, it's likely considerably higher quality than the W.E. kits. The only drawback is that you have to put together your own battery pack. The Ampedbike kit also includes brake levels that provide a motor cutoff. This would probably be nice to have, but it's definitely not a necessity if you're just running 36 volts. My brakes are powerful enough to stop the motor even if the throttle did stick, albiet it would take significantly longer to stop with the motor pulling. If I was running 48v, I'd probably value those brake lever cutoffs a lot more.
The rear hub motor doesn't provide any gearing, it's the same performance as the front hub motor. It might be harder to find a frame to fit the rear hub, and you might have to tweak your derailleur to make it work with the new gear cluster. There's also a very uneven weight distribution with both a rear hub motor and a rear mounted battery pack. If you use lead acid batteries, your looking at about 25 pounds of weight which is usually mounted on a rear rack. Off road, I would much prefer a rear hub motor. When climbing on dirt, the front wheel can break loose. It makes your ride a lot more interesting. You can actually control a bike with the front wheel spinning, but it's a skill that I would prefer not to have to learn. It's only a problem on really steep dirt. Also, if you've got aluminum forks, most people tell you not to install a front hub motor. The torque of the motor can break the aluminum dropouts and your front wheel can fall off. Ouch.
From first hand experience, I can tell you that the quality of the W.E. wheels and battery chargers is marginal at best. The battery pack, controls, and motors seem to be good. The kit comes with a rather minimal but adequate set of instructions. I've not been overly impressed with their service so far regarding the battery charger replacements. If I had it to do over again, I think I would go with Ampedbikes kit because it appears to be better value, although a little more expensive overall. If you're on a budget and don't mind tinkering with stuff, the WE kit could save you some money and probably work OK after you've got the bugs out of it.