This is a site dedicated to Linux and so I am of course going to recommend the Linux Mint option. The look and feel will be much like the Windows 7 interface you are currently using. You won't need to upgrade your hardware. You will never be out of support. It won't cost you a penny. You won't need to buy extra software such as Microsoft Office. You won't get any viruses.
Recently Linus Torvalds announced Linux Kernel 3.18.3. The Kernel includes several bug fixes. Latest Linux Kernel includes new features, bug fixes and improve security. Updating/Upgrading Linux Kernel is recommended.