Texas does a lot of kolache; there's a lot of German and Czech mixing with the Mexican influences around. But for actual donuts, there are family owned places with their own recipes but I don't know about regional variations other than the fact that you can get a donut at some places which is about the same size as a dozen normal sized donuts. I've not actually gone out looking for donuts though, so there may be more than the unsurprising "everything is bigger in Texas" kind.