Ai no Gundan wins it for me: it's super catchy, its overall concept is better organized than Waki Ai J since the outfits and the dance match the title perfectly, aside from the girls looking 10000 times more beautiful thanks to the bright lighting and the contrast of colors.
Waki Ai J sounded like a total mess the first time I heard it, and it took me 3 listens at least to be able to listen to the transaction between the verses and the chorus without feeling like something is off, plus the amazing dance formations aren't well shown in the MV such as the "?" or the dance battle during the music break.
Both songs are extremely epic though, who would have thought that Morning Musume who was releasing dull yet pleasant to hear songs a couple of years ago is now creating amazing performances through their songs, dance and MV!!!
I approve of all the Mizuki and Sakura love too