For the most part, most of the certs are 128bit. So it all comes down to how many browsers will reconize the SSL cert as a Trusted Cert.
For example, the $19.99 chained SSL at Ev1 is 128bit, but only
Internet Explorer 5+
will show it as trusted, the rest of the browsers, Opera, etc will display an errorm or some other message.
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Pretty much all of the SSL certificates are the same.
What I consider important is browser recognition and good support backup if needed.
I use Comodo certificates which use the GTE Cybertrust root, and don't believe what sslreview says as that site is actually freessl.
The root is stable and Comodo have told me they have an agreement to use this until around 2013.
It doesn't matter which browser it is, simply look at the root store and see if the root certificate of the provider your looking at is in there, if it is then that root is supported by that browser, quite simple really.
Some certificates are cheap because the validation of ownership is slack (remember Versign issued a certificate for microsoft.com to someone who had no right to have it, slack validation) whereas the Comodo validation is a two step process and carries a warranty for mis-issuance.
Not sure on the other as I do not use them.
In my opinion, Comodo certificates are cheap yet trustworthy and stable, they also have a pretty good technical support team when I need them.