Like everyone said, it really depends on what you want your layout to be.
The classic is tubular. If your looking for a classic toy train look, that's the way to go. But, one caution about that...its discontinued. There is still plenty of new stock but going forward, new will be harder and harder to find.
Fastrack and Realtrack are good for a "throw it down quick and has a semi realistic look" track.
Gargraves and Atlas O are (in my opinion) the most realistic looking of the bunch. But it takes a bit of work to achieve a proper realistic look.
