For your car I think the back is the only option. What kind of sub(s) did you have in mind? One well chosen 10 or 12 will be plenty for your car. The Crystals are a good choice, just make sure you have the space to mount them and a place for the tweeters and crossovers. Eclipse and JL are good if you want to pay for them. Check out
http://www.onlinecarstereo.com(low prices) and
http://woofersetc.com(high quality products)