It's interesting to debate the 2 vs 3 speed HST, but since you say your land is sloping I'd say that would push to go with more gears rather than fewer. But I agree with the guy who wrote that the transmission was only one of the things to be considered for slope work, and not the most important one either. I've been working tractors on slopes for over half a century now and I've almost figured it out.
The big thing to be concerned with on slopes is slope stability. Tractors were designed for flat land; so we pay special attention to lots of things to use them on slopes. Using any implement and especially a loader on a slope is one of the problems... you can do it, but have to be careful because as soon as you lift the implement or loader bucket the center of gravity goes up and things get real tippy.
We do what we can. Get a heavier tractor with a lower center of gravity. It has to have 4wd because tractors don't have front brakes....
Implements come in various widths and weights, go for smaller, lighter implements. When choosing a loader bucket you may want to consider the smaller ones. Smaller buckets and implements mean a larger proportion of the the tractor's total weight is staying on the ground instead of being lifted up. Keeps the CG low. While you are looking at buckets, my own preference is for the SSQA type mounting.
Tires make a huge difference on slopes. They are probably the biggest positive change you can make for slope work. You and your tractor will be happier with the lowest, widest tires you can find with stong sidewalls. That probably means that you want industrial (R4).... or possibley turf tread (R3). Both of those are way more stable than the traditional lug style Ag tractor tires (R1).
You'll want to decide on tires before ordering buying the tractor because tractor tires are not only expensive, but each of the different tires requires a different size rim, and the overall diameter balance between front and rear tires needs to be considered. Your dealer will know all this, or Kubota's "Build Your Own" tractor is also a good place to start. Some model tractors offer variable tire width; most offer tire spacers and wheel weights. Get every option you can find that lowers the center of gravity and widens the stance.
Those are just a few of the things to consider when you put a tractor on a slope. You can do it all, but it does take more thought.
good luck,
rScotty