I am not sure what standards apply to companies in this segment, but Comodo has an awful track record imho. Just looking at the Wikipedia article gives me a shill. And those are only the cases where Comodo couldn't deny any wrongdoing or failure.
One of Comodo's registration authorities was breached, but not Comodo themselves. Comodo were able to detect the breach and cut off the compromised RA because they were monitoring what their RAs were doing. Symantec, on the other hand, didn't know that their RAs were mis-validating certificates until I noticed and told them.
(Registration authorities are third parties that perform certificate validation on behalf of the CA. I think Comodo bears some responsibility for delegating validation to an RA that was compromised, but Symantec's conduct has been so much worse in comparison.)
