For me decisions are the better designed system. Let me tell you why, when a decision appears as a potential decisions for a country you get to know to two things, what you have to do to enact the decision and what happens when you do. As a player this is a good thing (especially for those major historical decisions designed to help your country go down a more historical path) because you don't have plough through a huge event file (and decode the scripts) to find out what is going on. Secondly I think this a more realistic system. Take HoI2 and the Sudentan Land after a few games you know exactly on which date this is going to happen, you get 20/20 historical hindsight. With HoI3 you just know it is going to happens some time after Austria disapears, which, for me, feels more historic.