Some would argue that the 42/43/4400 have issues. Complaints of HST transmission problems, front axles, and a few other things I'm forgetting. With that said I have a 4300 and 4400. Bought the 4300 first and while searching for a backhoe for it found the 4400 with less hours and a hoe already installed for a price I couldn't pass up. The 4300 will be for sale soon.
The 955 before it was a strong tractor, but they're even harder to find in good condition. The 42/43/4410 came next and introduced more computer controlled stuff like electronically controlled HST. They're nice but more expensive to fix.
I would second the recommendation to avoid the 4200. It's underpowered for its size especially if you want to mow with it and has a smaller hydraulic pump. I don't know much about the models after the 10 series, they were just coming out when I changed careers.
I was on the fence between a 955 and a 4300 when I bought my 4300. I had a lot of time on x55's but had never seen a 4x00 series before.
I don't know that I've heard of the HST transmission problems you're speaking of aside from the range lever selector shaft being easy to brake if you force a range changed with butted gears.
I also haven't heard of any front axle issues, are you talking about the ackerman angle tearing up grass? I personally think that's got a lot to do with how sharp you can turn it so people turn it all the way. It definitely seems to be able to turn sharper than anything else I've driven.
I really only have two major complaints about mine
My biggest complaint when comparing to a 955 are the fragile plastic hood and operator station covers. (the fender plastic is nearly bullet proof, no idea why they couldn't have used that on everything.)
Second complaint is the thermistor for the shutoff solenoid. I didn't know about it when it wouldn't start one winter day in a near-emergency situation, overdid the ether, and cracked a piston which sent me down a long road to a rebuilt engine. A $0.10 cent part failing, and my own ignorance of the problem cost me ~$1500 in parts and machine work and ~80 hours of my time. x55 series just used the starter to drive the peak coil and virtually no problems. This is how mine will be getting rigged up.
Slightly annoying you can't run the front PTO without spinning the rear like with the x55's but I've never really had an issue with it.
Also a PITA to work on the engine. The tank is HUGE and covers everything which is great from an operational standpoint, but engine accessibility suffers.
Despite the shortcomings I mentioned, I must say I am in love with my 4300 and would never consider getting rid of it. Hydraulics are more than twice as fast as any x55, 3-point capacity is ~3 times a 955, you can road at 15.5mph in c-range, the extra width makes for a much roomier cab if so equipped, the 430 loader is stronger, taller, and easier on off than a 70a, and JDQA is critical for me. I switch from the bucket to forks a lot. Front axle is much larger and able to handle the loader weight well. The whole tractor weighs about half again more than a 955 though so it does compact soil a little more but the much bigger rear tires make up for it.
I think the x55 series was a better designed tractor, but the extra capacities of the 4300 more than make up for the head scratchers for me.
o-and if you can find a 4400 go for it, same as a 4300 but with a little bigger bore engine. There haven't really been any situations where I have felt it was underpowered, but who doesn't like a little more power?