We do have this
thread to discuss these things. However, because I am still not finished, I'll just throw in some stuff. Donkey Kong is one of my alternative characters. So, I have Samus, Pit, and Donkey Kong. (I needed a character who would be strong in defense and offense.) Donkey Kong's kind of game is close-combat. All his standard attacks are quick, and he needn't go in for the kill just yet to defeat his opponent. After all, that d-smash of his has KO potential.
Donkey Kong can keep himself distanced by his f-tilt or d-tilt. His neutral A, though while simply a standard attack, does increase damage really quick if you continue to get hit by it. One of the things you should worry about with Donkey Kong is his B attack. If it's fully charged, he will have a magic armor when he uses it. So, if you were to hit him, and he were to hit you, his attack would out-prioritize yours, and he wouldn't be flying, but you would. Since Donkey Kong's kind of game is close-combat, deal out some damage against him with Homing Missiles. Though this only does 5% damage, the damage builds up over time. One with common sense would know that even small attacks will eventually bring their downfall.
If you are in the air, be aware of Donkey Kong's u-air. It is a powerful attack and can KO you. I've done it to a friend of mine just last night. His d-airs are also effective, so don't take those lightly. Don't roll around Donkey Kong, either. His d-smash will cover both sides, and if hit, you do run into the risk of being KO'd. Simply space yourself, and if you have to get in close combat, use your jabs and f-tilts. I use the f-tilts, preferably f-tilts while angled down. This does 10% damage, which is an additional 3% versus the original f-tilt. It also has a tendency to cause your opponent to fly. I've done this many times against my brother when he plays as Ness.
One final word: Donkey Kong's Up+B recovery is poor. He flies horizontally, so if you can get him low off the stage, he has no way of returning.