For me, strength...beauty can get you some places in life, but when it really comes down to it there's not a lot of use for it except to temporarily please the eye. Strength can carry you through any obstacles and keep you going long after others would have given up. The right kind of strength, applied in the right places, can keep you going toward your goals regardless of what tries to stop you.
While I absolutely agree with the answers here and value strength more than I value beauty, it is a whole different matter if we are talking about inner beauty, which can sometimes be part of a persons strength. Well, the answer will depend on the question, since yours isn't defined to details I will assume that you are talking about outer beauty and agree with wychic and triosol.
As for why, well strength is something that can help you no matter what situation you are in, while beauty can only get you something for a limited time, and personally I wouldn't think I achieved anything relying on beauty rather than my own capabilities. Beauty is a gift, it is not something that we achieve, unless we are talking about inner beauty
Just depends what are we talking about here physical strength or inner strength? Physical beauty or inner beauty? Out of the four I would go with inner strength it's what keeps us moving and keeps us going when the going gets tough. It helps us through those bad times and rests during the good times.