Definitely Tropical Freeze for me. It's the most imaginative, has the best music, best level design and wonderful visuals. The only negative was Cranky Kong; what a lame character to play as.
I'd go with the original next since it made such a strong debut and neither DKC 2 or 3 surpassed it in any meaningful way (in fact, neither were up to par, IMO), and I really didn't care all that much for Returns.