Google doesn't care which type of SSL certificate you get. As long as the certificate works, Google gives you a very slight ranking boost for HTTPS. The certificate type doesn't matter, Google doesn't give better boosts for better certificates.
As far as coverage goes you can have any of the following. Googlebot can crawl sites protected by any of the following:
- Single site certificate
- Subject alternative name (SAN) certificates that cover multiple sites
- Wildcard certificates that cover a site and all subdomains
There are also various levels of SSL certificate:
- Domain Validation (DV) - Verification has been done that you are in control over the domain. This is the cheapest and easiest certificate to get. Free LetsEncrypt certificates fall into this category.
- Organization Validation (OV) - Verifies the documents associated with your business before issuing a certificate.
- Extended Validation (EV) - Verifies your organization, its address, and its contact information.
In my experience, the type of certificate doesn't matter for SEO. I use domain validated SAN certificates for my own sites and I have no ranking problems associated with them. I see plenty of HTTPS sites ranking in Google that use SAN certificates.
Google's John Mueller said that for now, certificate type doesn't matter:
From our point of view if you implement HTTPS properly then that's fine for us. It's not something where we'd say this specific certificate is good but the other one is bad. I imagine maybe in the long run we'll be able to differentiate it a little bit more, but at the moment it's really just either: it works or it doesn't work.
Even if Google does start differentiating between certificate types it is more likely to differentiate between DV/OV/EV rather than between SAN/Wildcard/Stand alone.