I just sold my JD660 tiller this past August. Great tiller! Used it to establish several horse pastures and three remodel jobs at my house over the past 8 years. Never a problem with it.
Agree with KB9UDE with the recommendations for Land Pride and KK, too.
Your 4600 should handle a 6' tiller very well.
Gear vs Chain.. really depends upon how much work you need to do and the types of conditions you expect to work the tiller in. If you're planning a commercial venture and plan to install lawns and other landscaping - I'd say that a gear tiller would be a better investment.
Homeowner with routine garden work and cleaning up around trees and shrubs - chain is very adequate.
More important than gear or chain drive - IMO - is a slip clutch versus a shear pin. Better quality tillers have a slip clutch.
A few things to consider if you come across a used tiller... the blades will wear just like an old pocket knife that's been sharpened and re-sharpened. The blade end will be narrow and pointed and the rest of the blade will be tapered down to the base which will be as wide as the tine was when new. That's a situation for broken tines! I think my old 660 had 32 or 36 tines and they were around $7.00 apiece - 2 years ago.
Check for chain slop or gear slop - raise the tiller and rock the tine shaft back and forth (full revolutions, if possible) and listen for the chain clanking against the housing. Look at the adjustment bolt on the chain case - if it's turned all the way in close to the housing - the chain is probably well used and tired.
The seals and the bearings on the tine shaft ('cause they're always in the mud and dirt) can seep and leak and fail. Rock the shaft up and down and check for play in the bearings.
Check the gear box and look for water in the gear lube, smell for burning, etc.
Check the u-joints on the pto shaft.
Best of luck.
AKfish
