Interesting that this topic comes up every now and then. As a smaller operator with 2 4 x 8 and 1 4 x 6 tables put together in a backward "J" arrangement and 2 independent loops, I used Lionel Fastrack. I found it to be easy to install, liked the way the sections lock tight together, and the built-in roadbed. The layout has been up and running for over 10 years now and I have never had any problems with it. It's also easy to keep clean, although I probably don't clean it as much as I should. Fastrack has been very durable and dependable for me.
If I were to build a bigger and better layout, I think I'd go with Gar Graves track and Ross switches. However, in my old age, I've become less ambitious, so will settle with what I have. 
