chelsea, I guess you know that most roostocks dwarf the tree? Semi-dwarf and dwarfing roostocks don't live as long as the original tree's own roots. The majority of the rest of the rootstocks are for doing well in clay that doesn't dry out or extreme conditions. or very small back yards. Some rootstocks are shallowly rooted and don't do well in drought conditions. Almost all rootstocks need water twice a week until the tree matures. Some rootstocks force fruiting a couple years earlier, but that doesn't mean you aren't stressing the tree before it has enough of a root system to sustain both fruit and growth as a young tree.
Apple trees can live to be 100 years old on their own roots, and actually have fewer problems. It's better to keep a large tree on it's own roots, pruning the branches to the size you want, for the sake of fruit production, than to limit it with rootstock, unless you've got extreme conditions.
In dry climates well-draining soil is easy to keep irrigation water from evaporating with thick mulch of mowed weeds, grass, straw, alfalfa, whatever you've got in a large circle around the tree, being careful not to put it within 3 inches of the trunk so rodents can't hide under it and chew the trunk. Plus you get all the advantages of soil improvement and weed suppression.
You'll get the best results with irrigation rather than drippers. Irrigate, which sends the water lower than drippers, but let the soil dry out for a few days between waterings so the roots are forced to go deep looking for water. If you give them easy water, they will stay shallow and require it from you, not find ground water or damp soil down below.
It's really sad to see a fruit tree start to fruit less and less at just 15 years, and then die.
But that said, if you want to experiment, here's a list with good descriptions:
http://www.boyernurseries.com/rootstocks.html
Mediterranean climate, hugel trenches, fabulous clay soil high in nutrients, self-watering containers with hugel layers, keyhole composting with low hugel raised beds, thick Back to Eden Wood chips mulch (distinguished from Bark chips), using as many native plants as possible....all drought tolerant.
