Living in the US I'll assume you're looking for a good home track. (I live in North Carolina).
If so, I would consider one of three; either a Scalextric Sport, Ninco or Carrera.
A lot has to do with the amount of space you can devote to your track and whether it will be permanent or not.
Carrera is the widest track and has the deepest slot, but the track is more brittle than the flexible track of Scaley or Ninco - not good if you're going to be setting it up on the floor and taking it apart often - not much of an issue if your circuit will be permanent. It also has a smoother track surface and rails that are less magnetic and less prone to rust. You can run 1/32 and 1/24 cars on Carrera track. If you have the space you may want to consider Carrera.
Ninco is what I decided upon. At the time Scalextric Sport did not yet exist (there was only what we refer to now as Scaley Classic). I liked the extra width of the track, the deep slot and the fact that it, like Scaley, the track is somewhat flexible. The track surface is the roughest of the three and I have to say in my opionion that is one of the system's biggest drawbacks. Some slotters like the extra grip, but I prefer to slide around the curves.
Scalextric has been around for a long time. There new Sport track is not quite as wide or rough as Ninco's, but can be configured in more ways as at this time there is a larger variety of track pieces. It is, however, wider than the older Scaley Classic track. I like the new border sections too.
So which track is best? The jury is still out. What are considered by some as benefits are looked upon by others as flaws. It all has to do with your own personal preferences. But don't fret - you won't go wrong with either brand.
You are coming into the hobby at an interesting time as new digital sets are entering the market. You may want to consider one of them in lieu of the above mentioned analog sets. So far Scalextric, Carrera and SCX have released digital sets. Ninco should be releasing their digital sets in early 2005. I won't get into all of that here. There have been a ton of threads regarding the virtues of each and anticipation of future products on this site under the "digital" section.
Hope this helps,