You certainly need to take both into account... YOU HAVE TO!!!
You don't need to plan how many creatures will you draft before you open ur pack. It is quite unrealistic to do so because you can never predict what will you get and what others around table will react.
but at certain point in the draft (at the end of second pack in a Z\Z\Z draft for me), you need to consider the composition of the deck, because, well, if you only get 6 usable creatures by so far and don't take any action in your 3rd pack and end up with only 8 or 9 creatures, it normally gonna be bad.in this case, you should know you need to pick creatures over other things and have at least 12 so-so to good creatures(that's my opinion).
the point is, you should know what deck you are drafting. You should know what you want your deck to be.There are times when you draft really good quality cards but cannot win, because the organization is too badly balanced.