Tropical freeze is fun, can be frustrating though, especially in co-op. I haven't finished it yet.
Wii Fit U: fine as a $20 upgrade with the fit meter. I like the height meter functionality, it's pretty accurate. I take it with me while cycling to map the height profile of my routes. (obviously steps don't translate while cycling)
Wii fit is good for a warm up, and if you add some weights and increase the repetitions you can get some decent results too. You could do all that without Wii fit, yet it's keeps you in a routine and tracks your progress. The balance games are fun but won't keep you entertained long.
I don't know it the free upgrade is still available, but getting it 2nd hand for the Wii is probably the better route. You can already do that version on the Wii U game pad in Wii mode, and all the exercises are the same. Wii fit U only adds some balance games for the gamepad and a bunch of simple useless 'dance' routines.







