I want to know what are the most popular tags with the most upvotes.
Like character tags like Renamon (despite being a race tag) krystal, the ponies, and more well known characters.

https://e621.net/tag?name=&type=&order=count

What I meant was, the tags with the most upvotes, characters, artists (zonkpunch too obvious), copyrights, ect. No common tags like mammal, canine, male or female, common race tags. I mean certain tags with the most upvotes on each post.

https://e621.net/post/index/1/order:favcount
https://e621.net/post/index/1/order:score

Use these and try combining tags in the search:

Ex: order:score Krystal

This will give you the highest scoring images of Krystal.

.. how could you tell whether that meant anything, though?

I mean, it wouldn't be hard to get the median number of upvotes for a given one-tag query -- you just get the number of pages in the query, halve it, fetch that page of results (with order:score added to the query string), take the (page_size/2)th item, and extract its score. Then you could do that for other tags, etc.. and establish a relative 'ranking' of tags..

But there is no saying whether a query having a given median # of upvotes actually reflects the popularity of *that tag*, rather than some common factor (for example, if big_breasts is relatively highly scored, is that because.. big_breasts is actually "popular", or because female is relatively popular and big_breasts merely does not negatively impact popularity?)

The most upvoted tag is miata_(zonkpunch) with an average of 1553 upvotes per picture. (It's also only tagged on one picture.)