These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
An early popularity poll, when only a few of the Inter-Middle participants were just introduced, has following characters in the top 10. Tenth is Erio, ninth is Corona, eighth is Caro, seventh is Lutecia, sixth is Nove, fifth is Rio, fourth is Einhart, third is Nanoha, second is Fate, and first is Vivio. It's impressive to see that Nanoha and Fate were still that popular (well, they are the original heroines), but more impressive are Lutecia, Erio and Caro, who are above Subaru and Teana.
This poll was started at the time, when the Takamachi family, Team Nakajima and the Forwards visited the Alpine family in Carnaaji.
The latest poll has also some surprising darkhorses among the Top 20. While it is not surprising that Team Nakajima are in the Top 10note Vivio is 1st, Einhart is 2nd, Corona is 5th and Rio is 6th, the other ViVid characters have Sieglinde, Harry and Fabia at place 8th, 9th and 10th, respectively. Micaiah is 12th, Olivie is 16th, Chantez is 17th and Victoria is 18th. However, the surprising darkhorses are listed below.
The three Aces are also in the Top 10, with Nanoha being 3rd, Fate being 4th and Hayate being 7th. This is surprising, since the fanbase seem to love Fate and Hayate more than Nanoha, yet Nanoha is ranked higher than them. But even more surprising is Yuuno Scrya reached the 13th place, who has only appeared in a single panel!
Three of the Numbers also made it in the Top 20. Nove is 14th, Wendi is 19th and Sein is 20th. Another StrikerS character who made it is Lutecia who is 15th.
Ixpellia reached the 11th place.
Hilarious in Hindsight: In the end of chapter 35, the translator makes a gag by letting Miura saying "It's my manga now, bitch!", after she defeated Vivio in the tournament. In Magical Girl Lyrical Nanoha The Movie 2nd A's Tribute Comic, all major competitors but Sieglinde and Fabia are cosplaying The Movie 2nd cast. They are later divided in the Mid-Childan and Belkan teams, with Vivio opposing the three other members of Team Nakajima, Miura and Harry. One could say, Miura is stealing her friends, too.
Moe: Nanoha always had a strong element of moe (before Force anyway), but ViVid really pushed it to new heights with characters making cutesy poses and winking at you every other page. Even twenty-something Nanoha and Fate are no exception. Looking only at the magazine posters and the artbooks you'll never guess it's a Fighting Series, and not some kind of ecchi manga revolving around cosplaying, hot springs, beaches, and generally dressing little girls as inappropriately as possible.
The Scrappy: The latest poll hints that Miura seems not to be very popular, despite she is basically the fifth main character and is prominently featured in artworks and she even makes it in The Movie 2nd A's drama CD and DVD Commentary. However, she is not included in the Top 20.
Also, it's mentioned at one point that the reason Vivio lacks many of the abilities she displayed in StrikerS is because her Linker Core was damaged during the battle on the Saint's Cradle. This could have been an interesting character exploration if we'd gotten to see Nanoha's reaction to having effectively magically maimed her daughter, but instead it serves solely as a blatant excuse to nerf Vivio so that she doesn't curb stomp the other girls in the tournament arc.