I have Harmon-Kardons (true 3-way) with tweeter and mid-range in the factory replacement size. These are in my convertible, so I don't have a package tray to mount them, and the backs are in the quarter panel location. These are driven by a Kenwood power head with equalizer and power amp. I'm not driving tons of power, just enough for a clean clear sound.
The best music comes from my single chamber Flowmaster race units and the twice pipes.