So the maps for splat fest are Kelp Dome, Hammerhead Bridge and Museum d'Alfonsino. (Although it felt like it was just the first two since that's all I played for over 2 hours!... I just played on the museum, I think it's a new favourite so I've been wanting to go to it the whole splatfest)
I swear this game has one of those Monster Hunter desire sensor thingies haha...
For popularity it's kind of hard to say, I haven't faced my own team so it doesn't look like we have a majority, but looking at miiverse it seemed to be pretty close and I feel like I'm seeing slightly more mountains than seas in the pictures. I'm pretty sure the popularity will be pretty close this time, maybe within 5 percent at most?
As for wins, I think it's usually hard to tell since I'm just one person in several groups. I think I currently have more wins than losses, but it isn't a big difference yet.