I'd say that the most important thing is what sounds good to you...
I've done systems in two Contours, and if I were starting from a clean sheet of paper, I'd look at the Boston RC820 6x8 component speakers up front and Boston RM6s out back, as they would make a well-matched set of speakers. Team these up with a 10" or 12" MTX 4000 sub in a type 2S (small sealed box) enclosure, and you've got more than enough sound for a typical Contour.
I'd echo sound_contour's statement about 6.5" speakers vs 5.25" speakers - you get better midbass with the larger units. In high-end 6.5" speakers, the Boston RC620s I have all-around in my car sound great; I'd imagine Infinity Kappas all around would sound pretty good, too.
A less expensive solution would be Clarion ProAudio SRS1653 separates up front and SRC5753 plate speakers in back, though you sacrifice a bit of bass with this setup.
On the low end, I wouldn't bother with components - you're better off going with something like Infinity 5257cf, where you can pivot the tweeter for good imaging, and the oversized woofer gives decent bass output.
Once you pick your speakers, I'd say that (other than making sure you have enough power to drive the speakers) EQ and tweeter placement are the two things which will have the most drastic effect upon sound quality in the Contour. I've used the Pioneer AutoEQ system in my past two Contours (currently available on their DEH-P9300 and DEH-P9400MP head units) with great results.
As far as tweeter positioning is concerned, I've found that mounting the tweeters on the door sails and aiming them up and slightly back (line of sight would be behind/through the rear view mirror, at the top of the opposite A-pillar) gives excellent imaging. To make this work, you'll need a tweeter that can mount at approximately a 45-degree angle. Suggestions would be to a) set the tweeters slightly dull, because this location is bright to begin with, and b) buy some replacement door sails (with the little plastic snap-ins) so that when you sell the car you can return it to stock.
If you don't care about returning the car to stock, there are portions of the forward upper door where you can drill a hole and mount a pivoting tweeter - just be VERY careful to pick your spot well, because once you drill, that's where the tweeter is for the life of the car. Given that you can mount elsewhere and not do permanent damage, I'd recommend against this option.
Ultimately, you have to trust YOUR ears, because you're the one who is going to have to be driving with your setup for miles and miles.
Best of luck!
Originally posted by nOsSvTcOnToUr:
i have a 95 mtx tour se and was wondering what kind of aftermarket component speakers sound good in the tour? I'm hooking up system up really so and i really need to change the front speakers cuz they are horrible