I have a customer who would like to load balance two Microsoft Exchange 2010 CAS Servers which are residing across two data centers.
Which is the best solution for this? Cisco ACE or Cisco ACE GSS or both?
Depending on the config, you could go with either ACE or ACE GSS. If you need DNS-base load balancing and presence, then ACE GSS will meet your needs. If you have a single point of entry, say Data Center A, and then redirect to Data Center B as needed, then the ACE can meet those needs.
Why would you want to implement a solution that is dead. The customer could just go out and buy an F5 or Citrix or even a Barracuda LB and solve their problem. At least it would work long term.
Its not a misconception its a fact. Cisco has halted any future work on their LB products in favor of a partnership with Citrix. They will only release bug fixes for ACE and GSS for a little while. If you search google for this you will find tons of article and announcements of this fact.