I see a lot of people with recency bias here (and "own clan bias"), if it's from the whole decade, longevity and actually looking at everyone and the whole period should count for something. This may be news to some of you, but the world and Warzone doesn't resolve around you and your clan.
Best Clan: I believe Masters has been among the best for the longest time, in the earlier years, before Clans were a thing, especially [WM] stood out. Lynx, Apex and 20 should all get a mention here as well for being consistently good for more than just one year I'd say.
Best Player: Combining longevity with skill: mod, Timi and HHH should be the top 3 I believe, not necessarily in that order.
In the early years, The Impaller was the absolute best, while dead piggy, Gui, szeweningen (whatever the spelling is), Latnox and MotD could arguably be considered on top of the game for a while as well. Often overlooked, but shout-out to my clanmates Yeon and Jackie Treehorn for both being very good for a very long time as well.
Best Diplomacy Player: I have no idea.
Best Mapmaker: Incaman and Ranek both made some very nice maps that have been used a lot. They were at or near the top of the map ranking for most of the decade. Lionheart belongs to this list if we take into account quantity as well.
Best Community Member: (1) Fizzer for creating Warlight (Warzone) and actually be accessible to players as well, regularly posting on the forums, hostings streams and playing his own game. (2) MotD for creating MDL, with a shoutout to others who created CLOTs and the like. (3) Muli and some other for the userscripts. (4) The moderators of the website for doing the thankless unpaid job of keeping us all safe from squiggles, bootmatt and other people trying to ruin the fun of others. (5) All the serious mapmakers, who spent countless hours making beautiful maps, there is no Warzone without maps.
Most Entertaining Forum Thread:
https://www.warzone.com/Forum/1185-doushi-topMost relevant from this post onwards:
https://www.warzone.com/Forum/1185-doushi-top?Offset=40Background: the ladder was basically a few weeks old and the topic immediately diverted to ... stalling. It's not entertaining per se, but very enlighting and interesting to read now, almost 9 years later. Nothing really changes in human behaviour, everything comes back.
Best Map: See best mapmaker