If you are going to be working on lawns of customers and not tear them up, the Power Tracs are a very nice choice. I don't own one but have had a couple of them out to the property over the last couple of years and they are very stable and will fit into pretty tight spaces. Ventrac is also a nice choice, perhaps not as versitile as the Power Tracs, but for its size it will provide a higher lift on the FEL. I'd recommend Steiner also, but I believe they have cut back their product line recently so I don't know that they currently offer.
All 3 of the above brands are articulated tractors that are 4 wheel steer & 4 wheel drive. All are unusual but very capable. They are also inherantly more stable than any rigid frame tractor.
Should you choose to stay with a traditional tractor, and keep it small/narrow so you can fit through garden gates, etc. Then I would consider something like the Kubota
B7610, the New Holland TC26DA (or its Case/Farmall twin). They are small frame tractors but have quite a bit of horsepower. The Kubota has 24, the NH has 26. That will give you more available PTO horsepower for running rear implements like a tiller than other small tractors that are typically about 20/21 gross horsepower.
I would also recommend HST transmission for its ability to work in tight places with a little bit more ease and a little bit more precision than a gear machine.
BTW a skid steer is a better machine for moving dirt than a traditional tractor. However a Power Trac will be the next closest thing. I'd venture to say a skid steer can move 2 to 3 times the dirt a tractor can in the same amout of time. I'd venture to say a Power Trac could ALMOST keep up with a skid steer. A tractor will lag far behind. I've used all 3. If I had to do it over, I'd seriously look at Power Trac.