One thing you'll find a lot of here is free advice, most of it good. The next most common thing is opinions, few of which are exactly the same. Everyone has preferences for this reason or that one.
Speaking as a guy with a few tractors behind or beneath me who has been trying to narrow down a choice for quite a while now, I encourage you to take your time, try a lot of things on for size (literally), drive as many as you can, try the pedals and hand controls for ease of operation, and think if you and the tractor will still fit each other in 5, 10, or 20 years. If you buy a new one, it can easily last that long with good care. I have two that are in the 30 year old range, one a mower and the other a tractor.
Tires and transmissions are a big source of discussion here, with good reasoning and strong opinions on all sides.
Using tires as an example, I finally decided that I need ag tires because I use the tractor in the woods and barnyard and for driveway maintainance, but don't mow with it. Traction is at a premium, especially this time of year.
You might want to keep your JDs, at least one of them, as a dedicated mower and get a CUT for other work. Either R4s, which look tough and macho, or R1s, which don't look so tough but offer better traction, will be much harder on your lawn than turf tires on a smaller mowing tractor. It depends on how manicured you want the lawn to be. If mine is more or less green and short enough to not hide a small dog, it's fine. /forums/images/graemlins/laugh.gif Other guys want a putting green for a front yard.
The best advice I can offer is to spend a lot time reading here and thinking about how you'll use the tractor. Personally, I'd check with anyone you see using a tractor in their yard and ask about how they like it, what they do with it, how they like the dealer, etc. As has been said, the name brands are going to cost more, but have a better track record in general. There are examples of the off-brand machines doing exceptional work, but most here tend toward the higher recognition, higher price, somewhat more feature laden hardware.
For most of us, these are tools that serve as big toys, or toys that are justified by being used as tools. Just like hammers, you can buy a cheaper one (cast iron head and wooden handle) or a very expensive one (ergonomically designed head machined from unobtainium alloy integrally fused to a guaranteed forever shock absorbing polymer handle). They'll both drive a nail equally well, so it's up to you to decide which one you want. Or just get a bunch of power nailers instead! /forums/images/graemlins/grin.gif
Incidentally, not too long ago I saw a hammer in a catalog for $239.00! /forums/images/graemlins/shocked.gif
Oh yeah, the other thing the guys here are good at is vicariously shopping for tractors. We love to help you spend your money, the more the better.