From what I've seen, the Wii U version seems to have much tamer stages, while the 3DS version has much wilder ones.
Also, since the topic for this was closed, I'll just post my "past stages" list here:
Just as an FYI, I'm of the belief that ONLY the 3DS version is getting Melee stages, and only the Wii U version is getting Brawl stages. I can explain that further if necessary, though it should be obvious.
Melee stages for 3DS: Jungle Japes, Fountain of Dreams, Big Blue, Poké Floats, Hyrule Temple, Fourside, Great Bay, Venom, Yoshi's Story, Onett, Flatzone, Brinstar Depths, Mushroom Kingdom II
Brawl stages for Wii U: Battleship Halberd, Luigi's Mansion, Bridge of Eldin, Pirate Ship, Frigate Orpheon, Lylat Cruise, Pokémon Stadium 2, Spear Pillar, WarioWare, Mario Bros, Pictochat, Shadow Moses Island