I spent a long time yesterday trying to unlock all of the partners and playing with different ones. I thought you might enjoy a tier list of the partners. I'm not counting the last 2 so it will only be ranking the first 15.
15: Klara/Avery: The only pokemon different between these two as far as I know is Scolipede. I don't have Shield but have looked up their team differences. I've battled with Klara once. I didn't do it again. My Zacian basically soloed because, 1, her team kept dying immeditalty, and 2, she spamed the dynamax button every time she got down to slowbro, which was quick. I know it also said Avery had a slowking and slowbro, i'm not sure what his other one is, but I'd guess it's about as bad as Klara.
14: Nessa: I would love it if she was a viable partner option, but she's just not. Golisopod having emergency exit doesn't help either, it just destroys toxapex instead. Dreadnaw is only semi viable, I say that because it's just so easy to kill without Giganatmax. Nessa, I really wish I could pair up with you again, but there are better options.
13: Milo: Milo would have gone before Nessa if he didn't have flapple/appletun. Flapple is tough to kill. It is very powerful with max wyrmwind, but again, the rest of the team isn't very viable. It's better than Klara though, she doesn't have any viable members.
12: Kabu: Yes, I know I've basically trashed the first division of gym leaders. But Kabu's performance is horrible for the tournaments. Oh, tip for if Kabu teams up with Peony, bring a fire type, dynamax, go to town destroying Peony with a boost for fire type attacks. His torkal aids you. His arcanine kills itself, and you can easily manipulate dynamax to Peony and destroy his centiscroch before it can dynamax, sorry Kabu, you're not viable.
11: Gordie: First off, his Shukle is trash. Second, his Tyranitar's ability can hurt you, despite it being a pesudo legendary, and third, his collasal isn't that good without dynamax. Trust me, Tyranitar is his best one if he gets to use it.
10: Bede: His Mawile is trash, Rapidash is semi good if you keep it alive, and Hatterene is his best mon. Why is his Mawile trash? Anything with a powerful move can one hit it. Rapidash is ok, but is almost dependant on pyschcic moves. It would be more powerful if it had more fairy power.
9: Leon: The only thing that even got him on the list was his Aigeislash. A dynamaxed fire type is the only thing that gets past king's shield for me. Don't even talk about how good steel beam is. If it's used correctly it melts the pokemon affected. The other two aren't even worth talking about comapred to Aiegishlash.
8: Peony: Peony is ok, not much to talk about, not that good though, there are better options.
7: Piers: Stuntank has a good ability, not his best member though.
Toxitricity is his best. Overdrive is SUCH a great area move. Obsatgoon could be better, not much to talk about with it.
6: Opal: Alcremie murdered the enemy. Togekiss is almost at that level. Her weezing is a good dual type. Not much else to talk about.
5: Raihan: Flygon's sandstorm is annoying, but it is still a good pokemon. Goodra isn't the best due to lack of speed. Duraldon is good when dynamaxed. I just wish he wasn't so cocky.
4: Mustard: His Mienshow is a great start to the team. Kommo-o is his weakest, but is still good. Urshifu is THE BEST dynamaxed. I don't know about rapid strike, but single strike is great with him.
3: Marnie: Morepecko isn't the best. It gets better with Scrafty, but her best one is Grimsnarl. The dual typing makes it nearly unstoppable.
2:Hop: His worst is dubwool, easy to 1 hit. Zamazenta is impossible to kill for the enemy. I've never had his inteleon on my team, because the enemy never beats Zamazenta.
1: Bea: DID YOU JUST ONE HIT ZAMAZENTA! Yes, her halwucha did. Whenever I team up with her it just feels right. Her Halwucha deletes the enemy, falinks is her weakest but easy to get around, and her Machamp is amazing dynamaxed. She also can one hit Leon's dynamaxed charizard with halwucha. Yeah, she's good.
I hope you guys liked my teirlist! I didn't include Melody or Allister since I don't own Shield but I hope you guys that do have shield can form your own oppinons of them. Have a good day! (Be mad if you want just don't kill me in the comments.)