I would use almost anything other than Lily of the Valley. It is relatively slow to establish but then becomes a thug - a horrible thug. Another drawback is that it starts going dormant early and looks dreadful in Aug.

I am not fond of Ajuga either but it does make a great ground cover. It is low so that it will not interfere when you are pruning/picking your fruit trees. It will take moderate foot traffic with no ill affect and would certainly qualify as a living mulch.

I will take your advice, peren.all. I do want to say I have seen lov used well in a few specific situations. One was a groundcover surrounding a very large magnolia tree all the way to the drip line where it met lawn. The owner said it was easily contained by mowing. When I saw it the lov was already yellow but dense and kempt so I thought it looked fine. I would like to know how cariousvfround covers compare in their thirst for water..

So long as the trees are not dwarf varieties, water competition isn't something I'd worry about. The bigger question is how are you planning on managing the trees, which will determine the amount of shade they produce. I haven't dealt with sweet woodruff (though I probably should), but of the others, the daylilies are the only thing that can handle sun IME. The others will burn out if they don't get at least a half day of shade.

Keep in mind you will have to be able to walk among the trees any and every time you do any fruit crop maintenance or utilization activities like picking, pruning or spraying - any underplanting that does not lend itself to being underfoot during these times will be a problem.