1. DKC 2
2. DKC 3 - I like most aspects more than 2, but it's the exchange of Diddy for Kiddy I didn't like.
3. DKC 1
4. DKC 64
5. DKC Returns
6. DKC Tropical Freeze
I didn't even bother finishing the last too games because I found whenever I played them I just wanted to go back and play the superior original trilogy instead. They lacked the fluidity and great level design of the original games. They should have just called them New DKC 1 and 2 because that's all they are, inferior later instalments.
The original trilogy is a classic, it was the best looking game series of the generation, some of the best playing games of the generation, the highest selling non-bundled home console game franchise of the generation, with DKC being the top selling game overall, and the game franchise that pretty much won the generation for Nintendo over Sega. In addition, the original trilogy revolutionized the gaming industry by introducing console developers to rendered sprites and backgrounds, particularly Square, who began experimenting with this strategy on SNES during Mario RPG and some other later games that never got translated to a European language, but mainly FF7 which got released in the next gen.
The original trilogy is still, to this day, three of the best 2D platformers ever created.
If the original Dev team was around today and we're developing the games instead of those ex-Iguana guys, I wouldn't be surprised if DKC would be bigger than Super Mario at this point.