Nginx – Does any Certificate Authority support both SAN and wildcards

Your users certainly won't know (or care) the difference between an EV cert from one provider and an EV cert from another as long as their browser has the relevant root certificates such that it will accept the certificate without prompting the user that there may be a problem.

An EV cert from anyone (that the user's browser accepts certs signed by) is better than a "standard" certificate from anyone no matter how good a name. The user will see the big-green-blob-and-text or big-blue-blob (or how-ever their browsers differentiate the type of certificate) - the vast majority will never inspect the details of the certificate including who signed it.

Whether the difference between an EV cert and a non-EV cert is meaningful or your userbase is something only you can decide/answer. While education on the subject is spreading most man-in-the-street users will not know (or care) what a certificate is never mind knowing the difference between an EV cert and a non-ev one, but if your target audience is more clued up on average an EV cert might make them feel more secure using your services. Having said that some people are learning that "big green block on title bar in Firefox is more secure than the smaller blue blob which is in turn better than no colour" so maybe EV certs will become more desirable in general soon.

First, SAN certificate = UCC certificates. They are both just certificates with the SubjectAltName field.

Second, a wildcard of ..domain.com won't work in most browsers. You will either need to get two wildcard certificates (one for *.sandbox.domain.com and one for *.domain.com) or get a wildcard certificate for *.domain.com and have your SSL provider put a specific SubjectAltName of ja.sandbox.domain.com. I think DigiCert and GlobalSign offer this.