Google is the preferred ad spot due to integration into phone searches. You don't necessarily have to spend money with them, but when someone searches on their phone for a car wash this is most likely where the information is coming from. The higher your ratings, the higher your ranking will be, but to get to the top page you're probably gonna need to spend money in a larger market. Personally, I'm old school and don't bother buying ads or actively managing a page with any social media sites(facebook,etc), but that is a personal opinion. It just seems like too much work for the return. I would not interact with yelp at all, I've seen many people complain that yelp turns into an extortion racket. Same with BBB.
Oh, you can also get a Google voice number just for your carwash. You can forward, have it ring multiple phones, etc and it will send an email transcription is someone leaves a voice mail. It's free, if you don't mind the invasion of privacy.