This is a very difficult question. I have a tendency to like elements of tracks rather that the whole thing. Some circuits have an expectation before you get there and riders feel obliged to like it, for example, Laguna Seca, Catalunya or Brands Hatch. Each of these have some great elements but they are not necessarily my favorite track. The Spaniards have some good ones and I really enjoyed Almeria for its elevation changes, blind corners and the combination of turns. There is no hiding from any of the drills at that track, you need them all. In Norway there is a small track called Rudskogen that was great fun. 1.1 miles with 11 turns, elevation changes and a huge amount of fun. Thunder Hill in California has a couple of great corners that keep on your toes every time you go through them as well.
I do have a soft spot for my home track here in New Zealand. Hampton Downs is very special to me as I watched it being built and I was the very first person to do laps on a motorcycle. Having said that I agree with Brouggy about the elevation changes and the levels of grip being awesome as well. If I had to pick one track I think I would go with Catalunya. The facilities are really impressive from the minute you drive down the entry road all the way to the restaurant on top of the pit garages. The food is awesome and the track is just a pleasure to ride. It is an awesome environment to ride in and just riding there makes you feel like a top level racer due to the surroundings.
Just give me a track, I don't care where, there is always something that is to like. Even if it is the road that leaves it.