I haven't seen too much in the threads about what covenant we should be going for. So i figured i would get the discussion started and share a little of my research.
For Raiders
I believe the winner here is the Kyrian. The steward potion is a great oh crap button and will help a lot with dispel/debuff mechanics.
The vesper totem has huge returns (1800 %SP in healing, and 900 %SP in damage) that can be timed with a lot of mechanics and it's stationary nature is offset by tanks and predictable add spawn locations for easy setup.
For Mythic+
I believe Chain Harvest will be the winner. It has some of the weaker damage numbers at 225 %SP and 600%SP in healing. However the takeaway is the teleport which i think will add a lot to cheesing/skipping strategies. With higher levels of crit (50+) it's cd becomes even with vesper and heals the whole party. It has synergy with tidal flows so I see resto using this a lot.
For PvP
This is not my area of expertise but i believe the Night Fae may be the ones to go to. The Soulshape abilities movement and teleport abilities are clutch for escaping/chasing enemies. Fae Transfusion is extremely strong and has potential haste synergies for added damage. It comes in at a whopping 1200 %SP if you can hit the whole 8 and would be strong in battlegrounds. Even at 750% SP in 5s that puts some pressure on healers and gives you the same amount in healing. Between the added mobility and burst potential this is my choice for a pvp centered shaman.
Honorable Mention/Solo Content
At first I thought the Necrolord would be the dominate one with each ability customized for each spec. with the maelstrom rework it may still become the go to for enhancement depending on how hard lightning bolt hits and whether there will be synergy to ability. Primordial wave has some potential and while it only lists 1 charge my guess is that echo will add additional charges allowing for bigger burst windows. at the maximum targets Lava burst will hit for 664% SP on top of the damage from PW comes out to 974 %SP. It's healing variant is also extremely strong and I believe between the flesh shield and the targeted healing focus it is a real contender for Mythic+. Being able to get half your health as a shield after each boss or whenever you have a few seconds between pulls is huge.
Considerations
Vesper totem requires the longest to get it's potential with a GCD to place the totem (plus eyeballing location) and then getting 3 casts off.
Haste scaling on Fae Transfusion is unknown, best guess is 1 tick per second so 33% haste would add an extra 400 %SP damage and also healing boost to the maximum.
Primordial Wave requires the most amount of setup. To get maximum potential multidotting is required however if they bring back the old ways of flame shock spreading this becomes on of the highest damage potentials out there in AE. Similar if they brought back the old riptide glyph the potential is cray cray. However since it only hits riptide targets chances are that target is already back to full health by the time you can combo this off.
If anyone has answers to some of my unknowns or helpful input please share