The answer to your question depends...........
What head unit are you using factory or aftermarket ?
How much of an Audiophile are you ?
All Head Units including factory & aftermarket will distort sound somewere between 1/2 and 3/4 volume levels.
If you were to hook up any deck to a Oscilloscope and turn up the volume you would see the signal starts to "clip or square wave" which is what causes speakers to blow or distort.
Me personally I always prefer aftermarket.
For speakers I think its hard to beat Pioneer there speakers are resonable and the tweeters are crystal clear. If you want high end go with Infinity.
I would buy aftermarket if you have an aftermarket deck (or are changing it at the same time) otherwise go with factory because you will change the resistance that the factory deck is looking for and might damage it.
92 Bonneville SSEi - Stock - Remaining repairs needed due to neglect by previous owner - ABS/Trac, AC.
Mods so far: Maganflow High flow Cat, Rebuilt */C
Future Mods: Interior swap for Leath, High Output Altenator, Crazy system, Climate Control swap & Custom Exhaust/Intake.
98 Dodge Stratus - Wifes Daily Driver
92 Dodge Shadow - My Winter Beater