It depends. If you're coming from 4.1.2 ROM... and going to 4.3... Titanium Backup will have issues because they changed things on where/how files are stored in 4.3... but I think there is a fix for TB somewhere.
PS
Never backup system data if you're updating to a new ROM. It messes things up. Just use the Backup new user apps & newer versions.
I used Titanium when I upgraded from 4.1.2 to 4.3 and it all worked well. Use Titanium for all user apps and data. All system stuff will be automatically restored from Google Play (i.e. Contacts and Apps, Wifi access points) the only thing you need to backup extra is SMSes. You can do this from Titanium (export to XML).