Hector and Ephraim have always been quite popular, they're some of the best protagonists in all the games so they don't surprise me. They also share some personality traits. I like them both.
Celica is okay but nothing very special imo. Guess she's pretty and had a game not long ago. Veronica quite surprised me, but I imagine she and Loki (the "juicier villain girl" as you described it

) were voted because people were curious what they'd do if a villain won, since they have to give us them as a playable unit now. Veronica has more characterisation that Loki, especially in the latest story chapters. And probably getting votes for being a "loli" too. I wonder if they will let us pick one of them for free again.
Also they announced that sometime soon they will let all players vote for one of the currently in-game units, and the one people vote for the most will be given for free to everyone. Hoping people go with Bride Cordelia or someone I don't have, but someone like Ike or Lucina will probably get it due to popularity reasons, probably the newest Ike.