I dont know alot about tanks, espacially not in BFA, but in terms of fun Paladin and DK will probably always have a high spot on the list for me (espacially paladins). I did try Druid tanking two times but almost fell asleep due to boredom, but Druids are most likely a solid choice.
Best overall choice VIA method as of right now is Monk. They rank it #1 for Raiding, and #3 for Mythic. They base it on self sustain, tool kits, and mitigation. They also make it very clear that picking a "best / top" class in a pre-expansion state is nonsense as everything is still subject to change.
IMO don't worry about the raid picks too much. If you are asking this question on mmo-c then you are not pushing top tier content, and despite whatever your tryhard b tier raid leader says, you do not need the "best in game" tanks to finish content at the pace most guilds attempt and push it. If you do care about Mythics though I would look at tanks that tend to do well in mythic scenarios like Death Knights. They do not rate high in raids, but they are #1 currently in Mythics, and will be #1 in BFA in mythics because of their tool kits. Picking a class that people know is OP in mythic/'s will probably help you get random group invites which will help you out a lot while trying to learn.
Also the ratings made by the top guilds could mean absolute squat, and Sco admits this in his video, as they are all claims still being made prior to the expansion even launching. Everything is still being balanced and changed so you are honestly best off just playing a class that you are comfortable with over what you think can perform better.
Your choice of tank won't matter much unless you are doing high level content - Mythic raiding and pushing high level M+. In addition to that, the "best" tank right now may not be the "best" tank in 6 months. Tank parity is in a pretty good place and has been for a while. Sometimes a specific tank may have abilities that trivialize certain fights, but that's about it. Focus on playing a class that you enjoy.
Monk is top for raids and good for m+
Bear is good for raids and okay for m+ until very high level keys,where they're not bad but don't bring enough outside of not dying,it's also very easy to play and mind numbingly dull
Blood is decent for raids and best for m+ (considerably worse and more difficult than in Legion,but still best for m+)
DH is worst for raids but very good for m+
All tanks can do all content and it'll only matter if you want to raid mythic while current or push very high keys,if you're okay with heroic raids and above average keys,just pick something you enjoy really
If you want to be able to do everything and you don’t care about being 1-2% better than the rest of the tanks than it really doesn’t matter. Outside of cutting edge content they are all fine, go with what is fun for you. For me it’s DK
Monk due to their unique mitigation might have the most uses, and vengeance has the bonus of bringing the dreaded magic debuff in cases where you don't have a havoc DH in your group. Besides that there is really not much difference, all tanks have been gutted to the point that besides 1 gimmik each most of the time it doesn't matter unless you are doing 0.1% content.