Unimogs, because you can't go any bigger.

What axles are best really depends on your application. Toyota's are probably the most popular swap. I'll list my views, which may or may not be correct.
Toyota axles are a nice upgrade, they are still relatively light and can handle up to 37" or 38" tires without a problem. Not to mention a ton of after market support and well as bolt on conversions for both Samurai and Tracker/Sidekick based vehicles.
I use a Samurai front axle with a Hybrid rear. After twisting the splines on the front end with a Detroit EZ-Locker I switched to an ARB with Calmini heavy duty front axles, haven't had a problem since with 33" BFG MTRs.
One Samurai in my club broke a rear axle and one of heavy duty front axles last time out with 31" Swamper TSLs, he is upgrading to a Dana 44 front and Ford 9" rear. Both are solid axles, can be made to work with just about anything. Custom offsets are available along with heavy duty upgrade hardware and a full range of lockers.
Reverse Rotation is a nice bonus, it allows you to lift your drivelines up and out of harms way and usually means a stronger ring and pinion, but you are limited in your ratio choices compared to a traditional setup.