The "best" way is of course the 50 gem draw cause it gives a free one as well (10+1).

But result wise, it doesnt really matter, saving up 50 can get one impatient easily.
My own experience was using single draws on the beginning, for grabbing decent units quicker (I even got a 6* from these) and now that I have a stable team, currently saving for 10+1 draws.