hey man these are just my thoughts on the two axle sets, ask 5 others and you could get 5 other views, the which is better, what are the differences etc are in a bunch of seperate threads around the site so worth grabbing a beer or two and searching the forums.
My view though......
Bully axles are BOMB proof out the box the Berg you have to spend money to get them to that level, gears, lockers etc are all upgrades that have to be done to a Berg, dog bones bend like butter on the Bergs so again need an upgrade,
BUT once you've done those upgrades the Berg is a smaller narrower gear case making the upper and lower links plus shocks a ton easier to place, less binding issues and so forth. They weigh in less than the Bullys unless you take a grinder to the bully axles and chop out a bunch of the extra beef on them.
The Berg axles from my view have a better vendor network, with axle tubes, steering mods, replacement gears etc all available and more stuff coming through all the time (read D-Lux thread about his first foray in MOA and you get the idea) knuckle weights, knuckles the list goes on.
There are some vendors making Bully parts aside from RC4WD, the delrin rear tubes I have for example, but as said they are BOMB proof so aside from CVDs and some knuckle grinding to get better steering lock you can beat on these right out the box and not invest in a full rebuild before you get started
The parts and vendor support for the Bergs, the lighter weight for the axles and the wider track mean I prefer the Bergs but as i've said a bunch of times in this tread i do love this Bully rig it's not a comp winner right out of the box how I have set it up but with some tweaking it could be. It's awesome fun though "thumbsup"
The Berg are V1 and the same for the Bullys.
Cheers
Darren