Do you use a Gmail or outlook.com account for email? if yes, use gsyncit with Gmail, or stick with outlook.com.
If no, do you use pop3 or imap? With pop3, gsyncit would be my choice, especially since its paid for as it syncs your current calendar with Gmail. Outlook.com adds another data file to the profile - if you used imap in outlook 2013, this would be good, but in 2010, it adds a 3rd data file. So... basically, gsyncit unless you already use outlook.com.