It's being long time since i visited and posted here,
Well I will admit she might not that popular anymore like during XY/XYZ airing day but that because the series already ended, but i feel she's still on the top (maybe? XD)
here's the source,
(From Dephender)
Bandai held an online poll about Pokemon merchandise a while back whee we were, among other things, asked which characters we liked and would like to buy merchanidise for. One of the questions listed a bunch of potential products and asked us which of them we'd be interested in buying, one of which was "A music box that plays DreaDrea, featuring Serena in her Tripokalon dress and Nymphia dancing".
So that upcoming Serena music box figure is specifically being made because people told Bandai they wanted one. That speaks a lot of her popularity
the Poll ranking made by japanese bout asking who they would like to see Ash travel with again, and Serena was on top 2
http://pokemon-matome.net/articles/138950.html
https://s.animeanime.jp/article/2017/05/11/33827.html
There was a ranking bout short hair anime and Serena was on top 18
https://www.animenewsnetwork.com/in...se-poll-ranks-short-haired-anime-girls/.94519
and we have this Serena and Sylveon figurine to come out in few months
and don't forget how Twitter explode during the last episode of Serena And Ash farewell scene xD , like Shoko Nakagawa said(one of the main host for Pokemon show) Serena change the history ( she said it on joking manner
)
But I'm not saying Dawn and May is not popular specially Dawn was my fav pokegirl bfore Serena, I still seeing lots of fan art of them on twitter