What is the best contact back-up software?

Hello! I do not trust Icloud (and probably never will due to several bad experiences,) so I sync my 2400 contacts with MS Outlook, via Itunes and it's always been great but I've recently switched from POP3 to IMAP. So I want to back-up my contacts before attempting to sync. There are many 3rd party apps but just as many have limits to the number of contacts they will sync and I cannot afford to lose any information for my business. Any help would be much appreciated!