Zoro and Sanji are the polar opposites of eachother. Each of them have their own unique personality; Sanji is a charming blonde french who was a amazing talent for cooking, he is also a womanizer and a flirt. Zoro however, he is a stoic, blunt, straightforward man doesn't seem to have an interest in anything but swords and training, although he can be sensitive deep down, same goes for Sanji. 

Once you met them, they both immediately fell for you in their own ways as you are their other end.