I normally look at the site
Crutchfield.com to see what they have and how they rate what is available for my vehicle. Sometimes I buy from them, sometimes I get the unit somewhere else. Since most of my stuff is old, I don't normally look at the touchscreen/navigation/etc stuff. Brand wise I tend to like the Pioneer products best. Just have had the best luck with them for quality and all. I also have used Kenwood products and a few JVC, but overall I still tend towards the Pioneer. Good luck there is a lot out there.