According to Kubuntu 14.10 official announcement, Plasma 4 is our recommended stable offering and what you get from the default download, but is now in maintenance mode. It runs the software you are familiar with and will be getting updates and bugfixes but not new features from now on. Plasma 5. The next generation of KDE Software is still a work in progress. You can test it and install it from the Kubuntu Plasma 5 image but beware it will remove your stable software. We love testers but no support is offered. If there are problems you may need to reinstall to revert back to Plasma 4.
Kubuntu 14.10 Utopic Unicorn Screenshot Tours