I have the Alpine 9815 in my Stang and love it. It's basically the 9813 with a couple more features and a nicer display. I'm very happy with it and it sounds great. I was a Kenwood guy before, but this Alpine has made me realize why everyone speaks so highly of them...they truly are great HU's.
Eclipse HU's are also great for SQ but they look pretty plain so if you are used to getting compliments then I wouldn't expect nearly as many with an Eclipse. Ditto with Nakamichi decks (those are pretty fugly). However, I didn't buy my HU based primarily on looks and flash--if I did, I would have chosen a Sony Xplod deck.