You can partition your hard-drive so you can keep both. There aren't very many virii/malware for linux (among other great features), but there is also not very much software available on linux compared to Windows.
If I had to choose one, I would use Windows. I have too much essential software that only runs on Windows. But if all you want to do is surf the internet, Ubuntu will be fine.
If I had to choose one, I would use Windows. I have too much essential software that only runs on Windows. But if all you want to do is surf the internet, Ubuntu will be fine.