I went with Kicker CS. The price was decent, install was simple, and the sound is very crisp. I did however purchase the Metra factory plug connector adapters, which made it nice and easy. I also went ahead and purchased a new front center channel speaker with 8 ohm to try and balance out the levels from the front dash tweets and the door speakers. There is a very noticeable difference in doing that mod.
"Do or do not, There is no try!"
2009 G8 GT
2004 Grand Prix GT2
2014 Cruze LT RS