Since I have the go ahead, I guess I'll do this quickly. I'll provide quotes at a later date if they're needed, but I'll be including a few where they're necessary.
The Valar
The descriptions of the battles against Melkor, makes it clear that the Valar are all somewhat within the same tier of power, as it is the Valar as a collective (minus Tulkas) that battled Melkor outside Arda, with only Manwë being given a degree of significance, yet it stands to reason that all of them could somewhat affect him.
However, there is a wide-gap between some of their member
The Aratar
The Valar are not equal, and we are given description of how the "Aratar" "The High Ones of Arda" are incomparably superior to all other Ainur, described as "passing beyond compare all other, whether of the Valar and the Maiar...".
Their number includes Manwë and Varda, Ulmo, Yavanna and Aulë, Mandos, Nienna, and Oromë.
These members of the Valar should therefore be considered far superior to their peers (I'll get to Tulkas), but we do then have some further internal divisions to go through, with Tolkien rather handily providing what is essentially a scaling chain for the Valar in the Silmarillion:
(NOTE: The term "might" is used to describe the Lords of the Valar, and "reverence" is initially used for the Ladies, leaving some of their number a bit hazy, but as might is later used to describe them in descending order later on, and the Aratar are described as chief in "power and reverence", it should be okay to infer that their rank in reverence, is also in might).
(NOTE 2: The Lords and Ladies of the Valar are only directly scaled in regards to gender, so in cases where other sources are not available, it's best to assume the husband and wives of the Valar are equal in might)
Manwë
As chief of the Valar, and the "Elder King" of Arda, descriptions given to him in the Silmarillion and other works makes it quite clear he is rather comparable to his brother Melkor (fighting him to an inconclusive result in the disputed accounts of Dagor Dagorath), such as in the Osanwe-Kenta, where the two examples given of the "Great Valar" are Melkor and Manwë.
For instance, in the Silmarillion, he is described as the "chief instrument" against Melkor in the Third Theme, where the discourse and harmony of the two clashing songs balanced out, giving evidence of his comparable power to Melkor.
Moreover, when Melkor is depicted as fleeing from the wrath of the Valar after the Breaking of the Lamps, Manwë's voice is given equal significance to Tulkas' footsteps, when Tolkien describes the fear Melkor felt, again suggesting his comparability.
In fact, according to Morgoth's Ring, one version of the lore stated "Melkor and Manwe were brethren in the thought of Eru, and the eldest of their kind, and their power was equal and greater than that of all others who dwelt in Arda.", although later versions seem to abandon this.
Lastly, Manwë is described as the mightiest of all the Lords of the Valar, automatically putting him at the top of the scaling chain for the Valar, outside of possibly the following.
Varda
Varda is described in a similar light as Manwë, with the two being the respective King and Queen of Arda after all. Whilst I can't find anything that directly states she was equal to her husband, the two are depicted as two halves of a whole, with her throne being level with his, and the two, when seated together, being able to hear and see everything in the world.
However, her debateable comparability to Manwë aside, she has some descriptions on her own that puts her within a similar tier regardless, with Melkor being outright described as fearing her more than anything, and her position as the greatest of the Ladies of the Valar, scaling her above all her "female" peers.
Ulmo
Described as the "next in might" to Manwë of the lords of the Valar. He isn't given too much more beyond that, but it is said that Melkor could not subdue the sea, making it possible that Ulmo is directly comparable to him in some capacity, although it's likely this is just referring to his superior control over the waters of Arda, but given Aulë could not stop his ravaging of the land, it is debateable.
Aulë - Yavanna
The next in might, I have little more to add, as the rest of their descriptions here are not really about scaling/tiering.
Tulkas
Tulkas is a strange one to scale, as we are outright told, which Valar scale in might, yet he is not included in the Aratar, and whilst this could be because he joined the Valar later than the rest, this seems unlikely, given the Aratar are described in power, not seniority.
However, that being said he is described as both the strongest and fastest of their number, meaning he is superior to all the other Valar in that regard, and likely all the other Ainur, given he physically overpower Melkor. However, a note should be made that Tulkas' striking strength is superior to all his other forms of AP.
Oromë
Outright described as physically inferior to Tulkas, (wih some versions saying only a little weaker) but he is described as the second most physically capable of their number.
More importantly, he is also described as being feared by Melkor making his possibly comparable, but in truth, the association with this fear to his hunting of Melkor's servants, and the fact he was the only active Valar in Middle Earth at the time, makes this debateable.
The others
After this it becomes a bit more iffy, as whilst a few more of the Valar are compared to each other directly, the rest are left unclear, and you'll have to group them under the Aratar/non-Aratar distinction.
In regards to the Aratar specifically, the non above-mentioned members of their rank should still be comparable to their above mentioned fellows, given their outright description as "peers" in might.
Conclusions on scaling
The generic Valar as they are okay in regards to tier in my opinion, as High 3A, Likely Low 2C is reflective of them being somewhat comparable to Melkor and the Aratar.
The Aratar in contrast should be at least likely low 2C, given both the sheer gap in power between them and their lesser peers, and possibly outright Low 2C given that several of their number can invoke fear in Melkor, but that will need to be debated below.
Moreover, Manwë should be outright Low 2C, given his ability to contest Melkor in power, and Tulkas should have outright Low 2C physicals.
Varda will need to be debated, as whilst evidence is available to suggest Varda is equal to Manwë, the same evidence could merely refer to equality in authority.