JD 4520

If I were you, I would look for a good used 4230. I have one with a cab and it is the most useful tractor on the farm. They are old enough that they are fairly reasonably priced. The quadrange transmission is also a big plus.

I also was thinking of buying a 4620 before I bought my 4020 with M&W turbo. THere are a few reasons I got the 4020 instead. THe 4620 is an ok tractor, but quite a bit heavier, and the front axle wasn't adjustable like the 4020. The 4620 has an intercooler along with a turbo, which will make more power, but also the tractor will use more fuel. The 540 RPM PTO was also a big plus for the 4020 for me. I guess it depends on what you want to use it for. For loader & PTO work and all around utility, I'd say the 4020 is better. For pulling larger implements like chisel plows & disks, the 4620 would have the upper hand. But one thing's for sure, the 4020 will hold it's value better, and be in more demand than the 4620! Just go to a sale with a decent 4020 and you'll see you for yourself.