I would nominate a sunstar 20! ---- power steering on them. hi-lo hydro, turning brakes, AND diffy lock! --- Simp. even offered a loader for this model. I have four 20's and an 18.
A friend of mine has a 7116 and the diffy section is known to shuck gears really bad. I know of 3 of them not far from here that did that, so IF it were me I would choose a little better model for loader and as Kevin said,--power steering is a must!---- makes a whole different game with it.
Another good one would be cadet 147 series, --- BUT no power steering on them. A guy down the road from us had a 147 with a loader on it that he used in his hog sheds. --- The front wheel bearings dont last long under hard use, so that will something to watch and replace them before they go completely out and damage something else.
Which ever model you chose,-- make your loader sub frame long like Bunkclimber says and you wont regret it. ---- these little tractors will generate a lot of torque with a loader on them and things have to withstand it.
here are a few ideas to kick around. --- I like the idea of the trailer stub axles mounted under loader front axles, --- that would end bearing failure in the standard mower axles!