OP Search Engine 1, result:
LuNa --> 54
ZoNa --> 37
SanNa --> 58
ZoRob --> 19
OP Search Engine 2, result:
LuNa: --> 150
ZoNa --> 99
SanNa: --> 155
ZoRob: --> 44
OP Route Search, result:
Let's thinking about what causes such...
Nami is Sanji's only -san. The other women is called with title -chan (Vivi-chan, Robin-chan, Conis-chan, Caimie-chan). A reader had asked about this on SBS and Oda answered that Nami is special for him and -chan is just for fun. So -san means Sanji respect Nami so much and treat her on the top of women. It is the biggest hint that Sanji treat women different, not love them equally as womanizer/gentlemen and perverted.
I had some example characters similar with Sanji in another shounen manga/shounen dorama:
- Do you know Detective Conan? Remember that however Kogoro Mouri is so womanizer/gentlemen, he can have a wife. She is Eri Kisaki.
- Do you know Kamen Rider Kiva? However Otoya is so womanizer/gentlemen, he can love someone deeply at the end. She is Queen Maya.
- Do you know Love & College manga? However Hachibe Maeda is so pervert and love all sexy girls and protect all of them, his heart only for one special girl during the story. She is Sakurako Tenmaku.
Sanji is Nami's only -kun. No other boys crew she calls with it. And, no more question about this. Japanese people know that -kun means younger boy, cute boy, or BOYFRIEND! Well, if it is not boyfriend, at least it means the closest person/boy. It is the biggest hint of Nami that she have a feeling and not for Luffy or Zoro, we just usually see how this couple were so onesided from Sanji's perspective.
You can refer to other animanga/dorama. For example:
- Once again, Detective Conan. Sato Miwako calls Takagi with -kun from the beginning (Takagi calls her with -san), but they're just partner/nakama in Police department. At that time, they hadn't declare love each other but Miwako had placed Takagi as the closest guy. She said she doesn't have boyfriend when her mother ask but she refuse Shiratori and wait for Takagi. Now, you know they had been canon couple.
-Once again, Kamen Rider Kiva. Asou Megumi calls Nago with -kun from the beginning (Nago calls her without any suffix). Yes that they are a partner/nakama as Fangire hunters but they always argument. Although Megumi always made annoyed by Nago's arrogance, she keep placing Nago as the closest guy. And at the ending of series, they get married.
NOTE: Miwako and Megumi never mentioned "LOVE", just implicit by their way of calling.
C'mon! What is Oda's purpose to make Sanji and Nami call and treat each other like that? Maybe we still don't understand the meaning exactly. But, Japanese people can feel about their deep relationship insight between -san and -kun, even it's the deepest I think.
Additional hint, just my thought:
Oda also give comment about SanNa fanart published on Usopp Gallery Pirate consistently that be loved by Nami is Sanji dream. Well, I place myself in fangirling fantasy (hahaha...) that it means Sanji's dreams is not only All Blue. His seiyuu, Hiroaki Hirata, had comfirmed that the reason Sanji joined Luffy is because of Nami as direct factor: Sanji joined after Yosaku told Luffy that Nami was in danger place (Arlong Park), before it, Sanji still confused about left Zeff and still refuse Luffy so Luffy told Zeff that he didn't take Sanji. So, I wish Oda had planned that he will make all crews' dreams achieved at the end of series, and that means Sanji will get All Blue and also Nami.
So, don't worry if SanNa fans in worldwide is less amount, it still hadn't proven anything yet. Okay, I ask, is One Piece is the top popular anime/manga in the world, or in the USA, like how it always break the selling-record in Japan? Japanese people now get crazy of One Piece, many magazine's covers are about One Piece, railway station paste One Piece pictures on the wall, even NHK TV Station that not air anime now make a talkshow about One Piece, etc. So if the answer is not, you could see who is more correct.