Note that you can have as a goal in Wii Fit to gain weight (or remain the same weight).
As to which Wii Fit, definitely go for the Plus. It's just $10 more and, beyond having the entire original Wii Fit in it (games AND exercises), it has 15 extra games, several more strength and yoga exercises, and really most important by far, you can set your own routines (you can't do that with Wii Fit, there are no routines at all in Wii Fit so to move from one exercise to another you have to move between menus, which rather spoils the mood and wastes time when you want to actually do some exercises).
Ah yes and the Plus has multiplayer (by taking turns) for some games.
Currently Playing: Shin Megami Tensei: Devil Survivor Overclocked, Professor Layton and the Curious Village
Anticipating: Xenoblade, The Last Story, Mario Kart 7, Rayman Origins, Zelda SS, Crush3D, Tales of the Abyss 3DS, MGS:Snake Eater 3DS, RE:Revelations, Time Travellers, Professor Layton vs. Ace Attorney, Luigi's Mansion 2, MH TriG, DQ Monsters, Heroes of Ruin
