About speakers, the following types are most common:
Dual cone: Most simple, cheapest ones. Consist of a Mid range driver.
Two-way: Consist of a Mid range driver and tweeter.
Three-way: Consist of a Mid range driver, Tweeter and Supertweeter.
Coaxial: Speakers that have all the components integrated into one unit.
Component: Speakers in which one or more components are separate from the main speaker body. (Usually the tweeters are independent)
Components give better sound quality but may not always be feasible due to space restrictions.
Pioneer A935h are also good speakers, but they are oval speakers so they won't fit in your doors. For the doors you will need round, 6 inch speakers. If you want to fit the speakers in the rear parcel shelf the A935h is a good choice.
The high-end brands do give great sound quality, but usually work best with an amp. A standard head unit often cannot power these speakers sufficiently, which is why you would be safe sticking with a mid-range brand.
RMS (Root Mean Square) power handling is a measure of the electrical power the speaker is able to handle continuously for a period of time. This should be no more than 75% higher than your stereo's RMS power output.
Peak power handling is a measure of the maximum electrical power a speaker can handle for brief intervals of time. As long as this is higher than the stereo's peak output, it will not make a huge difference to sound output.
Sensitivity measures how much sound (in decibels) is produced by a speaker when fed with 1W of electrical power and measured from 1m away. This gives a good idea of loudness, but not sound quality.
Impedance is the equivalent resistance of all of the speaker's components combined. Since you're using a stock HU, this should be 4 Ohms.
The strength of the magnet and stiffness of speaker cone can affect the nature of the sound produced by a speaker, but I would not worry about this too much in your case, no offense.