You will get 1000 opinions on this and any time you ask something so general. Best is hard to define.
What type of dirt are you seeing on them? What brand/model vehicle. Maybe a picture for an idea of severity would help us give you a better idea too. Try to be more specific.
Do you want something to use just on your vehicle or something you can get in gallon sizes to use on lots of vehicles? What level of cleaning are you looking for? Is it more of a maintenance clean to remove dust and fingerprints or a deep clean to remove embedded dirt and body oils from the surface?
It's a 2013 Chevy Cruze. Just bought it for our daughter. The headliner has some spots that I would like to clean.
The dash has a ring on it that I will take a picture of today. Just wanted to clean and freshen the seats for her.