The best 4x4 speed methods are Yau and Hoya (Yau is more commonly used). Just google those methods up. The best 4x4's are the YJ Guansu, Moyu Aosu, and Cyclone boy's G4. the YJ Guansu is the cheapest and requires little setting up.
The guansu may be a little blocky if you do not like blocky cubes however, if you would like a looser cube then the cyclone boys g4 is nearly as great as the guansu. (i have not tried the aosu)