OK, some things off the bat.
This list I am about to make will probably be criticized, and rightfully so. This is just a judgment from someone who has played all four games, but hasn't come close to mastering a couple of them. So, by all means, correct me where you feel I am wrong. I encourage it.
I will now list achievements in order of my personal ranking. I will not touch the records. I have no interest knocking over that beehive nest.
So, here we go. List from hardest to achieve to easiest to achieve.
1. 1.3 million on Donkey Kong (It's the Holy Grail of this series)
2. 1.6 million on Donkey Kong Jr
3. 1.2 million on Donkey Kong (I can imagine some might say this is harder than getting 1.6 million on DKJr., but you don't have to play the game nearly as perfect, and you don't rely on RNG
4. 800k on Crazy Kong (I'll be honest, I'm not positive about this one, but it feels about right)
4. 1.5 million on Donkey Kong Jr
5. 1.1 million on Donkey Kong (I was tempted to put 1.4 million on Donkey Kong Jr, but I realized that a lot of new scoring techniques have made this a whole lot more doable)
6. 1.4 million on Donkey Kong Jr
7. 1.3 million on Donkey Kong Jr
8. Looping/rebirthing the 256 boards on Donkey Kong 3 (Easy Settings)
9. 1 million on Donkey Kong
10. 700k on Crazy Kong
11. 1.2 million Donkey Kong Jr (I was tempted to rank this below 900k on Donkey Kong, but you don't need much point pressing to get to 900k)
12. RBS on DK3 Easy Settings (Yeah, screw it, I'm biased)
13. 900k on Donkey Kong
14. 1.1 million on Donkey Kong Jr
15. Killscreen on Donkey Kong
16. 1 million on Donkey Kong Jr
17. 900k on Donkey Kong Jr
18. Killscreen on Donkey Kong Jr
19. 600k on Crazy Kong
20. Killscreen on Crazy Kong
Yup, there you have it.