I prefer down on first and fourth beats,but will sometimes play six quavers ddu ddu,or ddu dud.
I prefer to play two downs if I am going to a string,further away from the body,but sometimes for variety I will play this string up.
it is fun to sometimes try and start on an up beat, Sully suggests this at the beginning of lark in the morning udd udd.
I think the ideal must be to be comfortable in any direction.