You have your answers :
There are lots of things to consider to say someone is attractive. The way someone talk, walk, move, look. Here Sanji is not even top 3 for the male audience, for girls only two times out of 5.
There is a huge gap between them.
Zoro and Luffy's personnalities, charisma and probably physical attributes are way above than others.. I am not into guys so I don't know what criteria should be taken to consider who looks handsome.
But I assume most of people find Zoro more attractive and it's not even a dual.