Tropical Freeze of course. It's like the equivalent of Galaxy 2, NSMB Wii, etc., in that it took the same engine and ideas and such, and expanded them to new heights. A lot of similar concepts in the levels, but more refined and more interesting, plus new water levels that actually worked pretty well for the most part. The music was also much, much better than the original game. The graphics are better too, though that one is partially attributed to being on a more powerful platform. Even so, the art style seemed a bit better.
The only negative I would have is that it has a few less levels, though on average its levels might be a bit longer than in Returns, so it's no biggie. Some "neutrals" I guess I'd call them, is that the bosses still drag on way too long, and the multiplayer wasn't improved any and doesn't work that well.
I am still on the last world of Tropical Freeze, whereas I've spent way more time with the first game... wouldn't be completely fair to vote yet, but I'd say that Tropical Freeze does seem to be an overall improvement in most ways, and the addition of the HD visuals, new characters, and amazing David Wise soundtrack sure help!
Donkey Kong Country: Tropical Freeze without a moment's hesitation. Returns frustrated me to the point of quiting, while the controller had to be pried from my hands when playing Tropical Freeze. The only niggles I have regarding Tropical Freeze are the boss fights. They were repetitive and boring. Everything else, a blast.
It's pretty close. I guess I'll give it to TF since it pretty much took care of the very few flaws of Returns (blowing mechanic, forced motion controls, forgettable soundtrack) and made the stages even better.
Returns for me. Better hidden puzzle pieces, better difficulty balance, and there aren't 1-2 extra Kongs stuffed in that feel like they're made superfluous by a third Kong. Returns feels fresh. Tropical Freeze just feels like an expansion pack.
Granted, the visuals and music favor Tropical Freeze, but those are small enough pieces of the package for me that they don't override the rest.
@Zero I bet a lot of reviewers docked TF a little bit for not being as fresh. I mean it is pretty much a repeat of Returns except with much better graphics and animation and controls and gameplay and level design and music and fun and whimsy and basically better everything.