jimmyj - welcome back buddy!
Lifting 500lb round bales on the 3PT will be more comfortable for either. The 4x5 round bales I was using last year were definitely more than 500 lb btw. I think that my L3400 could have done it fine with another bale at the back. Another member here (mahana) has some pictures on his site of the L3400 with rounds - in the front and back.
I like both tractors. I have a L3400 as you know. I would be right on top of the dealer about the 3 pt valve jerkyness on the L3400. Seems like they might have gone back to the old jerky valve. They replaced mine under warranty. Other than the valve, I'd say the weakest link in the tractor is the cable operated PTO. All of that said, I have had 0 problems with my tractor and I still have the old PTO cams.
All of that said, I'll bet the snot has been tested out of this tractor in the field - they sell a LOT of them! I'll bet part of why we know about all the weak points of the tractor is because there are so many in use out there - many times more than competing models like the CK30.
The CK30 is a really nice tractor. I operated one and didn't think that the 3PT valve was any less jerky to be honest... at least not after the upgraded valve on mine. Some nice touches that the CK30 has over the L3400 are the telescoping rear links. The factory rear remotes on the CK30 are a very clean setup using hard lines vs. the L3400 is basically an aftermarket setup (even the factory one!) that they jack the price up on.
If I had to decide between these two models - frankly I would go for the GL3240
It beats both these hands down and is not a lot more money.
If I were forced to decide between these two, and I knew I would keep the tractor for a long long long time - I would go with the Kioti. The fact that the dealer in our area (guessing you will be dealing with Dick Lott) is top notch compared to pretty much every Kubota dealer I have encountered within a 1 hrs drive would heavily bias the decision for me more than anything else. There is no doubt in my mind that the Kioti will depreciate faster and when you do sell it - 5 or 10 yrs down the line - you will get less for it - at least around this area. They are not unknown but Kubotas are legendary. Like I said - base it on your time horizon.
Both are top notch tractors and hard to go wrong with.