RE: Which one
Like alot of issues regarding axle strength here, I disagree....a little
The AMC M20 has a bigger center section, carrier, and ring gear than a D44. The factory shafts aren't good for 31s, but moser makes high strength replacements. I'd put a set Moser 29 spline shafts against the factory 30 splines in a D44 anyday. That leaves the tube weakness as the only downside when compared to a D44, and a full truss will fix that. I'd take a modified AMC 20 anywhere I would take a D44, and I'll throw 38s on a D44 in a heartbeat. But it wouldn't be bulletproof by any means. I've got a M20 sitting in my storage building that was toting 39s at one time.....and it's still in one piece. Just for fun, I tried to blow up the one in my CJ7 before I swapped it out. It's still got the two-piece axles, and I couldn't break them. I gave up when I decided I would have to risk blowing the engine up to destroy the axle. I know if I had some slicks I could have pretzled it. It kind of sucked. I even gathered a little crowd to watch the carnage, then I'm sitting there with a built V8 and 36" Swampers......and I can't break a little AMC20.
With the CJ D30, I've had and seen others have good luck up to 36s if you keep it unlocked. I've seen several people with 38s mounted to them, but that's a little much. 33-35" locked, depending on what you're throwing at it. Just keep a close eye on those joints and replace them with the best you can afford AS SOON as they start to go out.