@Spoonwood owns the #1 and #2 Standard Deity 20k spots with outstanding dates, so I don't think I'll touch that.
Those were not my first games on Standard Deity 20k I think. I believe I had high position on some of those Deity or Demigod tables before the current entries that you see. At the very least, I'm sure that I had some upper level 20k games of my own which I took off the tables, after looking a little more, and refining my approach. I also got more confident about spawning a leader, since I learned/developed the capital landing strategy on an archipelago 80% map.
But still, after that I remember some attempts on Sid which looked like great starts. Then one of my deliberately weaker research opponents decided to land on my shores early, and I quit. We even tried a Sid succession 20k game on an archipelago map and tried again on another map, but again got invaded.
Perhaps most surprising on those tables is that the #2 Sid 20k game is only 17 turns behind the #1 map, but got the #2 game got played on a 60% pangea map instead of an 80% archipelago map. I did not expect to end up that close to Kuningas for my pangea game (I also didn't build one wonder).
Huge Deity 20k might be the weakest of tables, but I think it's kind of different. I don't think I prebuilt with Carthage. I don't recall that game at all. I do remember though that after say a curragh and settler, or soon after, with a strong enough map, it ended up possible to not run out of builds in the capital. But, that seemed more difficult if not impossible on a Huge map during the ancient age, due to increased tech cost. Trying for The Republic slingshot also struck me as more risky. And 8 opponents as the minimum implies someone as scientific, commercial, seafaring, or industrious I believe. That said, I don't think an optimum map would need to use the 2nd city with palace prebuilding on a Huge Deity map, though such is the more sounder strategy for sure even if slower in some exceptional cases.
Most of the Sid games didn't have the full, self-researched Republic slingshot, though the 1750 Large map did, if I recall correctly. I had extra commerce somehow, and it worked. I think maybe one other time I pulled off the Philosophy, trade for Code of Laws shot, take Republic slingshot, but I also recall just taking Monarchy as a free tech, and then later revolting another time to Republic.
Also, I would hope that you feel free to just submit any game that will chart instead of giving up on a map for some reason.
I remember watching Soren Johnson's talk and him saying that their vision was that the human player win the game on the last few turns. With that in mind perhaps the greatest 20k game is Elear's 2045 AD finish on Tiny Sid with The Byzantines. I haven't looked at it, but as great as number 1 positions may feel, I believe that players who finish later on weaker food and production maps near their starting tiles may be the stronger players.
Anyways, mapfinder generated starts may be the most fun to play for you, so do as you will in the end.