I think that a lot of Sanji-Zoro rivalry among fans are caused by the said characters themselves, as they always are bickering about their power levels.
But in manga, they are also bros who rely on each other and trust each other, and will support each other when needed, while still bickering, of course, because that's how their relationship is being portrayed. They're both friends and rivals and they inspire each other to grow strength-wise.
I like Sanji because I like smart characters, I like his unique fighting style, and I like how loyal he is (even his leaving the crew was basically to save the crew from BM), and I also like his overall character complexity. Yeah, I am not happy with the perv gag, and the scenes of Sanji being beaten by women, but character flaws make characters more human.
I like Zoro as well, and what I like about him is his unwavering determination to achieve his goal, and his trust in Luffy. His fights are usually very cool, and he does get a lot of cool moments. I also love his gag of always getting lost, it is not overused and when it gets a highlight, it actually is funny.
So to me, both Zoro and Sanji are great characters, and I don't want to downplay any of them. I would rather have them shine even more, so that they overcome their chicken wings status and become truly great powerhouses on par with Luffy (who sadly is the one character I start to dislike, especially in his Nika mode).