Alicornutopia

I'm not sure how you would define "smart", since people are smart in totally different ways. But I'd be interested in seeing you rank Bells in the order you define as smart.

Cuteness seems pretty subjective and age dependent. Shell Bell is super cute, I'm not sure there's obvious standouts otherwise.

For some reason I feel like I've done smartness before, but I'll do it since I can't find it. I am not including pure speed boosts or things like perfect recall that Bells acquire on pealing (or equivalents, like vampirism). So this is mostly mediated by childhood educational background and access to things to read/learn and how it affected the Bell's development (early access to magic or another huge passion-trigger helps, high peer quality helps, improved parents help but not very much by themselves, scientific worldview helps), and in a few cases the likely gene quality of the population from which they are born. I'm not counting Lorica at all because her tinker powers are an awkward confounder. Smartest to least smart; high tail is longer than low tail:

Linya
Glass
Tab
Aegis
Cam (Cooper)
T'Mir, Chi
Loki
Eve
Ice, Dreamer
Phoenix
Katie, Nika
(middle of the pack)
Sylvi (etc.)
Promise
Sarion, Clarity
Cymbeline, Kiri, Shara
(anybell not elsewhere listed from a vaguely medieval setting)
Shell Bell
Stormy
Ace, Rapunzel
Spring
Aya (Sphere)
Aether

Why is Ace so low? She seems like she’d have a lot more resources, better peers,scientific worldview, etc. tham Rapunzel, with whom you have her tied. Is this something that would be obvious to me if I knew more about Pokémon? The only downside I can think of is lack of unusual magic (unless you coubt the legendaries she isn’t certain exist) and lack of educational institution (maybe, I’m not sure about that), but that doesn’t seem that extreme.

In Pokémon you can get your license to acquire 'mon and go tromping around in the wilderness when you are like ten. Ace did. She hasn't had much school; she reads, but in a kind of undirected way. Rapunzel had kinda few books, but not much else to do but read and think about them, while Ace can sit on a bird and fly around, and do battles.

Why Cooper is so high? Higher than T'Mir? Also I would expect Revelation to be higher than Cooper...

The Speech helps, as did dropping out of conventional schooling to study wizardry, and Cooper got access to it earlier than Revelation got any of his advantages (using summoning is more about being careful than about being especially creative, and by the time Revelation died and had lots of free time for self-study of miscellaneous whatever he was already an adult). T'Mir got a nice futuristic education but with no magic and a chunk of her time taken up by having to learn to fit in acceptably in two different cultures instead of just one. Chi got a nice futuristic education but with her magic being martial-arts instead of intellectually oriented, same-ish deal.

Willingness to share thoughts, notebooks or equivalent with specific third parties (I’m thinking of Shell Bell handing her recorder to Sherlock vs. one of the Bells not even being able to imagine willingly having Gracenote).

For those that use a visual medium and in-their-head cryptography for thoughts, information denstiy and difficulty of cracking the code. I’m thinking that Aya/Pring probably win here on both counts, but I’m not sure.

Bells in general may share curated segments of their records with people; this doesn't vary. Shell Bell's recording had locked segments that Pearl would have needed specific per-occasion help to access. I can't remember which Bell said anything about not being able to imagine having Gracenote, which suggests that the remark is more circumstantial than anything that might warrant producing a spectrum list.

I don't have detailed codes worked out for the Bells that encode, and there's also a distinction between the ones who process in code and don't diary at all (e.g. Aya, Aegis) versus the ones who do diary but in cipher (e.g. Loki, Butterfly) that I don't know how to collapse into a single list.

Is Golden the only Bell who (had) an aversion to the smell of blood? If so, why didn't that become a Bell attractor? If not, could you rate that on a scale?

Bells in general have this (Juliet mentions it a few times) but it doesn't come up very much for most of them. It's not interestingly varied.