Honestly, your best bet is to actually stick to the classic rum and coke. Vodka works too I guess. The shot to coke ratio depends on a lot of things. First of all, how big are YOU or the person you are serving. If you have a 5'3" girl who has never drank in her life, you best use one shot, or even a half a shot. If you are 6'4" then you are safer using like 2. You will pretty much always taste the vodka, or at least the after taste. But its not as unpleasant as whisky or something. It doesn't have that cough medicine after taste.