If you're looking for OEM approved, the best providers have very patchy coverage. Dealer.com and DealerOn have absolutely archaic UIs and are painful to manage your own content. DealerInspire currently is easiest to manage given it's wordpress but word is that's going away.
If you want a more modern site infrastructure you're gonna have patchier coverge, but the better we have seen we would group together in no particular order as follows:
Team MXS - Modern SPA React, expanding OEM coverage.
Team MXS | Dealership Website, SEO & Marketing Services
Space Auto - Modern SPA React, expanding OEM coverage. (Definitely the most advanced interoperability we have seen)
https://space.auto/
Overfuel - lots of rave reviews and a modern CMS. Good performing sites but no coverage on your OEMs and we have only seen them a few times.
Overfuel | #1 in Dealer Websites
Motive - Modern but somewhat rigid designs and good/expanding OE coverage
Home | Motive
Team V - Modern but somewhat rigid designs and good/expanding OE coverage (probably the only that covers all your brands)
Apollo Sites | Dealer Website Platform | Team Velocity
If you are only chasing OEM approved for Coop, you are jumping over dollars to pick up dimes. Go get a good website and you won't care about the lost coop.