First we need to know what your budget is and what you’re looking to get out of the system. Do you want your music to be just plain loud or are you looking for sound quality and balance? What are your daily listening habits (genre, volume, and time spent listening).
So many factors can influence what is recommended to you and while members here can help you in the right direction, it’s best to do your own research to get what YOU want out of your audio system.
PartsExpress’ website is an amazing resource for browsing quality drivers and has something for every budget out there.
P.S I assume this is going in an old VW bug based on the headunit selected and I’m not sure how strong the factory alternator is but I assume it will not be enough for a high power system but that’s okay, more power isn’t always better.