What is the difference between 3 way, 2 way, and component speakers? What is a decent amount for wattage for rear 6.5" speakers?

 

2-way speakers have a tweeter and a mid-woofer. A true 3-way would have a tweeter, midrange and woofer with each driver having it's own crossover filter. Cheap 3-way (and higher) car speakers are nothing more than a speaker with multiple tweeters. There is no band pass filter for the midrange driver so it is essentially reproducing the same frequencies as the tweeter. A quality 2-way is all you need.

Component speakers come with a much better crossover network. Most co-axials and tri-axials run the woofer full range with a capacitor connected to the tweeter to block the lows from going to it. A component set uses a high pass section for the tweeter and a low pass section for the woofer. Co-axials and tri-axials only have a capacitor as a crossover which has a shallow rate of attenuation of only 6dB per octave. Component speaker crossovers usually have at least a 2nd order crossover which attenuates frequencies at 12dB/octave. A 3rd order crossover would attenuate frequencies at 18dB/octave.

 

What he said. ^^