Alright, guess I'll reply more seriously.

1. BlurredD - A Bunch of very user-friendly and high-quality tilesets, as well popular and versatile levels. Also his work and effort on jj2+ and other stuff is worth a mention, although that isn't JCS-related.

2. Evilmike - That's it. Five very high quality single-player episodes of the same serie, and lots of other episodes/level packs/levels that clearly stand out.

3. Kejero - Tomb Rabbit has to be one of my favourite single-player episodes too, eventhough it's hard and frustrating at times. Shockingly great storyline, and a greatly different standard of gameplay, considering what kind of other episodes were several years ago. Also a few good, but unpopular tilesets(that are for TSF though.)

4. FireSworD - Do I really have to explain? Jungle's Edge that was just FireSworD's tryout level for OLC, became one of the most popular multiplayer-levels ever. And it of course didn't remain as the only one. Even today, he continues to create as inspiring and fun-to-play levels as before.

5. Blackraptor - He wouldn't have been nro 5 otherwise, but since I saw as a betatester some of his latest work, it really impressed me. Of course, he has been a great JCSer in the past as well, but his latest work is something special.

6. Ragnarok - Well, what can I say? His works have been so far very successful, as in satisfying a great majority of players with the gameplay in his levels. Of course he has been creating only multiplayer levels, but the way they work out in real games is outstanding.

7. CelL - Started out as an average level creator, although his levels were considered great with the old standards in the past. But his levels gained quality and more of fun-factor progressively. After all, he has done a lot of work to give people some absolute classics like Zaitox Station 67, or All Your Base CTF.

8. Snooze - Well, the amount of work in the time he has got is amazing, and lately it has been very outstanding. He has been working already for a long time on levels of his 'New Ages'-serie. He has worked on both SP and MP levels, although more specially on MP. There has been both uphills and downhills. For example take New Ages I, which was a great surprise for everyone, while New Ages II, was sort of a disappointment considering how good the previous one was, at least for me. But in overall he is one another outstanding JCSer.

9. cooba - Several high-quality levels with variable game modes/themes/sizes. Also created the excellent Waste Treatment Facility-set that has been accepted very well by the community.

10. stripe - Has been inactive for years already, but created several "hits" during his time. Happy Semiconductor being the most known one, is one another of the most popular multiplayer-levels out there. Also Superconductor and Happy Castle(JAIL) were some other fairly popular and great levels, although not as much as the 'semi.' The rest of his levels were still good, or around average, but due to these he is my nro 10.

EDIT: Also I forgot about Violet, but I guess I'm too lazy to edit that anymore now though. He would have been somewhere between 6th and 9th probably. Also note that I didn't list anyone who was more focused on tileset-creation here.