I'm not that familiar with the handheld ports from the series except maybe for one that came out for the original gameboy. I wasn't as thrilled to play it as a kid compared to DKC on the Super NES, which the game blew my mind away as child for it's amazing presentation at the time.
Unfortunately I never got the chance to play DKC2 and DKC3 on the Super NES, though I did manage to try out DKC2 on the Wii Virtual Console. In results, I loved DKC2 more than DKC1. I haven't tried DKC3 yet, though I'm thinking of getting that game next when I have the time and money to purchase it.
As for DK64, it's a pretty fun game, but I'll say it's the hardest game from the franchise. This game led me with so much fun times and sometimes frustrating times where there's a lot of backtracking to do and some nearly impossible challenges you got to complete. It's not my favourite from the franchise, but as a 3D platformer, it's quite decent.
Then there's Donkey Kong Country Returns which this game really surprised me that DK went back to its recognizable roots that fans loved from the first DKC1, providing with some fresh and neat ideas to make it fun and challenging. My only complaint I have with this one however is those riding rocket levels. They practically drove me nuts as I progressed later through the game. Other than that, it's definitely one of the better recent DKC games that ever came out after DK64.