Ugh, I really dislike it when people call them maps. they are circuits, racetracks, theatres of speed, whatever.
Depending on the car, depends on the circuit. The Nurburgring 24hr layout is good for a lot of things, but I also enjoy Le Mans, Bathurst and my own personal favourite circuits - Spa-Francorchamps. Silverstone is great fun for a really, really quick car like the Red Bull Standard, while Monaco, Tokyo and Madrid are pretty good fun in road cars with plenty of power and no traction control.