Budget?
You say you want a "great" system... That's a relative term. If it's sky's the limit, then you're gonna want separate speaker components all the way around with custom enclosures, dedicated amps, in-dash navigation, Bluetooth, multiple screens, game system, etc, etc, etc. If the sky is not the limit, you'll need the basics of good speakers (either full range or mid-high), a good subwoofer with a dedicated amp and a nice head unit. Whatever your range... Go for quality over quantity or features.
I could ask for your musical taste but truth be told, that really doesn't matter too much. The components you chose are either going to (on a sliding scale) reproduce well or not. So long as it sounds good throughout the frequency range, any music you pump through it should sound the way it's supposed to.
If you want good advice (even if you don't buy from them), check out Crutchfield. They've always been a wealth of good information, especially for the novice...
https://www.crutchfield.com/lc_3/Car-Audio-Video-GPS-How-To-FAQ-and-Shopping-Guides.html?lcg=3