If you are looking for full support from Microsoft for quite sometime, than Windows 8 is what you should use. Mainstream support from Microsoft until 2018 and Extended until 2023. Windows 7 ends 2015 and 2020 respectively. As for the touch screen aspect, Windows 8 is designed with touch in mind, so navigation would not only be fun in metro but also intuitive.
Aside from the start menu and certain upgraded system tools (Task Manager mainly), I barely notice the difference. I like it, and would recommend it for a brand new system