Wonda because she seems to have come first and been the original mascot. Also, her name is a play on "Wonder" - it's too good! Wonda's Wonder Festival. Wonda Festival!!
Also in the earlier artworks she has brown hair and looks like a regular, everyday girl, if a bit tomboy-ish. I enjoy the tomboyish-ness that she has. I love how the earlier artworks show the two engaging in cosplay activities; either they are cosplaying or constructing costumes or props themselves. It's so cute.
I find it interesting that Reset's earlier artworks show her with pink hair, but at present she is a blonde and instead it seems Wonda has taken over as "the one with pink hair". I kind of miss Wonda's brown hair, ngl :(