Very common question and there has been a lot of talk regarding the AMC20. If you look back 2-3 weeks through these posts, you will find them. Regarding the AMC 20, its a good axle if you make a couple of mods. Its strength is the large ring and pinion. Its weakest point are the flanged axles but these can be replaced with 1 piece solid axles. Others say the tubes are weak. In my opinion, a couple of tack welds on the tubes should take care of the tubes turning. If your driving your jeeps so hard that you bend them, then you must be jumping hills.
I just completed a rebuild of my AMC20 by adding Superior one piece axles, 4.10 gears and an ARB. If you are running 35's I hope u have at least 4.10 or higher gears. The Dana 44 or 60 are good upgrades, but unless they already have the gears and lockers your want, you will spend as much if not more getting it in your jeep.
If you replace the axles (about $300) and your gears, you will be in good shape....unless of course you want to spend lots of money.