I start doing the gates asap. They are all lvl based so if your a lvl 2 your enimies will only be a lvl 2.the higher lvl you are the better stuff you get.I very much enjoy doing the gates. They randomly open up everywhere. On the other hand my husband hates doing the gates so he gets the main mission out of the way. Once the main mission is done the gates are gone forever.
I go ahead and do the missions in Kvatch then I get Martin to Jauffre.Once I do this I hardly ever do anything on the main mission until much later.
It all depends on how you play the game.