I bought a used 4300 last fall so Ill try and provide some info. 2000 JD4300 Hydro w/ 430 loader: 675 hours, Turfs, $12,500 from local dealer.
Ive got about 100 hours of mowing, loader work, box blading, brush hogging, raking and snow removal.
I have been very pleased with the tractor overall.
Positives:
Hydro is great for mowing, loader work (primary reason's I purchased)
Very comfortable operating station IMO
Plenty of power for my needs. Friend has a 4200 that he uses for similiar tasks and loves the 4200, the only comment he has ever made is he wishes it had a little more hp which the 4300 has.
Turfs have been fine for mowing, snow removal and loader dirt work 4 wheel drive makes a huge difference- (would prefer R4's but new rims and tires are cost prohibitive at this time)
Upgrades:
My tractor had the issue with the battery acid at some point in it's history, cleaned up the tray and underneath replaced strongbox battery with yellow top optima
I am having an issue with my 3pt resetting- have read about it here and am working towards a fix (adjustment, leaky cylinder or valve). 3pt leaks down slowly while running until position control senses the change and brings it back to orginal position. Hasnt kept me from any work, but is getting annoying.
Apparently there was an issue with the hydraulic filter going to the rockshaft getting dislodged- fix was issued by JH with a new improved filter and some re-routing of hydraulic lines at back of tractor (can read about this here- I did)
Vertical stabilizers for 3 point are a pain in the butt when hooking up 3pt attachments- will be changing over to horizontal stabilizers in the future.
Overall very pleased with the 4300, I would buy again. I liked the idea of the mech. hydro over the electronic but am sure that some of the features on the ehydro would be great to have (loadmatch, etc)
Hope this helps and good luck with your search for a tractor.