The two main reasons why I prefer to stick with an online tool:

I don't have to carry an extra notepad+pen with me. I can easily copy and paste long urls and click on them

When I am not in front of the computer, I use my iphone to write down ideas and tasks and I update my online tool when I am back on the computer.

For those who want to stick to paper and stay minimalist: http://www.pocketmod.com/

For those who want an online weekly planner: http://weekplan.net (my own tool based on the 7 habits)