I guess this is not a correctly asked question - SSL certificates normally are being issued for a domain, multiple domains or subdomains (wildcard). So if one installs a certificate on the servers' hostname and shares it, other users (on a shared server) could use that, but only by accessing their website through servers' hostname. Of course it is better to have your own SSL certificate issued only for your domain(s).
There are also different types of SSL certificates: eg. Domain validated, Organization validated, with Extended validation (EV), etc. and cheapest (only EUR 11.99 /yr.) could be only domain validated - Cheap SSL Certificates
Hostname SSL: Should be used for services like Control panel URL, Email services, etc
Domain SSL: Used as they defined and used based on a individual sites.
Here, this can be categorized for all clients in following ways.
Shared servers will have one main SSL i.e the hostname SSL that can also be used a Shared SSL for customers who cannot afford a dedicated SSL.
All VPS or Dedicated server clients can make use of this if they have a business critical email.
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Symantec is definitely the most respected, but they are also the most expensive. Comodo will provide the same encryption, albeit much lower warranties, for a cheaper rate. Comodo certs are definitely the most popular with our clients.
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