We went to FtW the first time in May 2003 and were assigned to the 1600 loop. We also rented a golf cart and took an afternoon off to explore the other loops. When we found 1900; specifically 1918 we knew this was home for us during future trips.
1900 seems to be the last loop assigned and so seems emptier than the others. Makes sense since its the last full hookup loop in numerical order. But its more than that. Even when its full, the sites seem more private with more space and trees/vegetation between you and your neighbor. They also seem a bit longer and, depending on how they are situated on curvier parts of the main road are easier to back into.
Don't feel shy about asking for what you want. On each of our subsequent visits we got 1918 twice and the site directly across from it once because we requested it. During that trip 1918 was occupied when we arrived and vacant until nearly the end of our 2 week stay. I could have asked to move, but once I was all backed in and set up I decided not to bother.