Escort/Passport 8500. Best in the market right now. I've got mine hardwired into my fuse panel adn run up the side. Nice clean install with no unsightly wires to get in the way.
A word about the cordless detectors though. They usually only have about 1/2 the range of a good corded model.
The bst right now are the Bel 936, the Passport 8500 and the Valentine One. Choose wisely and remember that this is an investment for you. Buy it right the first time.