So I had a really solid chat with my Multiplayer circle over the weekend and we put our thoughts together based on 12 games we've played as a group since GS came out.
I think it's important for a "tiering" system to have context, considering how hugely subjective the subject is. So for reference, this is based purely on the opinions of 8 people and our Multiplayer experiences from only 12 games, it holds no baring for AI matches, nor does it take into account the Civ's flavour/music etc.
Too strong
Maori - Overtuned. And ironically, possibly due to the conservative streak that Firaxis has that tends to undertune other Civs. It's possible they thought the radical start would disadvantage the Maori to the point where they needed substantial perks but it's possibly too much. Mana has more in it than some Vanilla Civ's entire kit. He is quite vulnerable early (including one hilarious match where his settler was blown up by a storm). but if he can land and dig in, he is STRONG
Very Strong
Hungary - His ability is odd because it's either RIDICULOUS and unstoppable, or completely inconsequential. He suffers more in MP as people are wiser to his tricks and save envoys for his assault. However, his mere presences means that you need to be conservative with city states and play the game more warily in general, while he can freely and quickly build his infrastructure, which is why we think he is still pretty strong
Strong
Phonecia - Dido is nasty, she comes out the gate quicker than you would expect and her expansion is rapid. She is the richest Civ in the first two eras and if you are next to her you will have a city plopped next to you. Invulnerable Quadriemes and a Coastal city makes invading her tougher as you only have a few tiles to safely attack her from. She has a fast open game, and a ridiculous end game, but she has a middle lull where she is trying to expand where she can be vulnerable if she spreads too thin
Kristina - The theming bonus is very solid and OAM & Queens Biblio is very solid/ Kristina can be quite remote and still be effective, which is irritating as an opponent but effective when you are playing as her. The Caroleons were slightly underwhelming, I thought they would be more fearsome when they appeared (similar to Garde Imperiale, which is very strong at first appearance), but they are still a solid UU. She's just solid, if a little unexciting?
Ottomans - They can be fearful warmongers but their war bonuses come online slightly late, so you can prepare for him. The Janissary is a wretched unit to go up against (sorry my bias, it's really strong haha!). When he starts taking cities down, he holds them well and it's harder to get them back. Also Ibrahim can be quite a foil to Dido and Eleanor shenanigans, and the combat bonus is not to be underestimated. He's good.
Good
Inca - I think the Inca is much stronger against the AI than in MP. Their UU is quite easy to keep in ZOC and vulnerable to attack, their mountain ranges are amazing but leave them fairly vulnerable if placed improperly, their cities are incredible but they rely on mountains which means where they are going to be predictable, and generally wide is better than tall (and all of these things are what make it premier against the AI, but we haven't seen it play out in MP)
Mali - I think the Mali's potential is probably the strongest of all these Civ's but in MP he just never gets there. He got a Desert start in less than 20% of our games, and the production malus REALLY hurts when he doesn't have the food/faith from the desert. Additionally, being slower to put up a military in the early eras makes him quite vulnerable, but he can absolutely rip a new one if he gets going
Eleanor France - Not to be underestimated, you need to be very careful with war when she is nearby. Taking another city or city state when she is around will almost always flip to her. However, this tends to mean people start with her so she needs to build a sizeable defence, which slows down her cultural game
Needs help
Canada - I think everything that needs to be said is being said, the big difference is that their cities tend to be razed instead of kept because they are tundra. I suspect they are quite scary later on but they rarely made it there, sadly.
Eleanor England - There's a bit of a disconnect with the abilities here, and the RND seems much uglier without Pax Britannica...
I really think all the Civ's are pretty great to be honest, but we all agreed Canada could use a little love.
Again, this is not authoritative (at all lol) as we've only scratched the surface of the game. Additionally, we are not "uber" players or anything. We've all beaten deity but we are far from optimal. But I thought it would be fun to share our thoughts