I use all three as well. Calendar is the winner for me in what takes top priority. Whatever is on there happens. Email is the winner for taking up time. I spend a lot of time there communicating and planning. Todo lists, for me, are a bit sloppy. They are just things I don’t want to forget about and I want items on the list to bug me until they are done.
What is missing for me, at the moment, is a more forced priority system.