Having a bit of techie background - I'm all for having an electronic planner that you can effortlessly sync your phone, laptop, tablet etc. In theory great but when it doesn't work - not so great.
However, I use both. My phone syncs with my computer but I also use a paper diary - I resorted to this when I had problems with my phone not syncing to my computer. I prefer to write things down and the more tactile nature of a pen on paper. Not only is it a lot quicker writing down an appointment than scrolling through the options on a phone but I also use my paper diary for my action list and notes.
Yes you need to keep them both up to date but it only takes a few minutes each week and you can make it part of your daily planning time.
What's your preference?