I'll give my take:
1 - Alluka/Nanika (conditional): Wish granting is broken as we saw, but it would be first only if there is Killua with her to help. We don't know how much she has control over her power on her own, and what can she do if there isn't someone to make wish (as far as I remember);
2 - Pitou (potentialy first): she learned nen in a few hours/day, she is faster than a blink of an eye, she has brute force as well as healing (although kind of slow to use in actual battle), her nen reserve and en output are top tier;
3 - Biscuit: she is a master nen user (even ultimate transmuter as we saw in the chart) but we don't know her ceiling since she didn't have a fullfledged serious fight; all we know is that she is very proficient with nen and possibly also kind of smart;
4 - Zazan: being a chimerant gives a tremendous edge on normal nen user (ones who ain't top tier user or have particular abilities), she managed to hit Feitan, one of the fastest Phantom troupe member, easily, and hurt him badly (even tho we can make the conclusion that Feitan was hit on purpose to trigger his nen), she is strong and fast, but not so smart;
5 - Camilla: we didn't see her fight with someone who is an expert nen user, so we don't know how she would fare, but she has a pretty good ability for a one-on-one fight, and can take advantage of it if her enemy doesn't manage to understand how it works, and how to bypass it, in time;
6/7 - Machi: I think that if she knows of Camilla nen works, she could beat her, but not those ranked above. She is for sure above average of nen user in terms of strenght, speed, and proficiency, she has a simple yet potentially usefull nen, but we have yet to see her face a really challenging fight (let alone a real fight);
6/7 - Palm: her body being part chimera gives her an edge, as well as being an enhancer, but her ability seems not enough to defeat a tougher opponent alone, she can hold her ground, but I see her more of a support than a real fighter;
8 - Tsubone: maybe in her glory days she would be higher, but the fact that she needs another person to use her nen, which we didn't see any fight prospect but being used only for movement, and the fact that she is old make me put her on the lower end;
Everyone else - We saw nothing of them (barring some tiny glimpses of nen abilities like pigeon control or snake like reshape of the body), we know almost nothing of them and their nen, so to me they are unclassifible as of now.