There are probably as many answers to that question as there are quilters. I tend to do a lot of wallhangings, where the durability of the threads is not important and I tend to select them by color options. If I am making a large quilt that will be washed often O tend to use either Gutterman or Mettler. They are both expensive but never break and last a long time.
I was just looking at the website of Superior Threads (www.superiorthreads.com) and in the Education section they have a guide for the threads they carry that is great as an orientation of what to use each thread for and what needle to use.
Maria