Should I uninstall the Salesforce Connect for Outlook before installing SalesDesktop?
Actually, you should use only one solution at a time. The reason is clear: The Connect for Outlook and SalesDesktop sync the same data between your Salesforce.com account and your Outlook independently. This will cause duplicates in your Outlook. So, the best way would be to uninstall the Connect for Outlook first. Note that after you uninstall the Connect for Outlook, all records that have been added to Salesforce.com such as contacts and tasks are still in your Outlook folders. So, if you install SalesDesktop right after uninstalling the Connect for Outlook, you will get duplicates for all your downloaded Salesforce.com records in your Outlook.
