GD 140, a1a
It doesn't have really deep canyons like pomeche or ariel, but it has some really great canyon fields with turns everywhere you look, and a station extremely close to the planet for quick returns after rebuys. I started out thinking deep canyons were amazing, but honestly they're pretty boring now. GD 140 a1a is easily my top pick for canyons at speed.
Viper 3 is the only way to go if you like canyons + speed. ieagle and courier can also get high top speeds, but neither can match the vipers boost ( multiplier or length ), and at those speeds you can't turn effectively without it. That is what makes the viper shine.