Face first ! I can't throw a flag over and fulfill my duty for the fatherland (as we say in germany).
Second: overall body proportion (petite prefered)
If first and second is OK: The magic triangle is my heaven to go.
The real question is how big can small boobs get until they are no longer small. I'm ok with larger tits I just dont like really big ones. IRL its nearly impossible to get a nice natural pair of big tits on a woman who doesn't weigh 220+ pounds (that's 100kg for the rest of you).