1) The "best" is very suggestive. Might as well have asked what the best beer is, or pizza, or religion, or *gasp* motor oil...
2) There are several great threads on this forum with details of folks doing exactly what you're thinking of. From mild to wild. Pretty much everything you need from part numbers to wire break outs. Seriously, this forum rocks! Lots of great information stored here on the threads.
3) Crutchfield.com does a pretty good job with prices (not always the cheapest, but most of the time they are) and does a pretty good job with it's "fitment" section.
4) The consensus is stay away from big box retailers (like, BestBuy) since they may not be the most skilled technician working on your car. Don't get me wrong! Some locations have top notch installers. But, you take your chances when you use their installation shop.
5) DIY is the way to go.