I would like to throw @c-squared witness into that hat, I may be biased as one of the cofounders but I feel our curation record more than stands it own against the others mentioned, and c-squared is far more inclusive both in terms of what sort of content it upvotes, and who can participate as a curator - c-squared empowers everyone to be a curator on the Steem blockchain, join the Discord and request the "curator" role to begin helping out with the curation effort! Currently c-squared has dedicated curation teams in English, Spanish, Dutch, Filipino, Italian, Turkish, Burmese (Myanmar) & Indonesian languages. With well over 200 curators, I believe @c-squared is the largest manual curation effort on the blockchain. All posts curated through c-squared are resteemed on the @c-squared account (which also follows the authors), and a daily selection of ~10 posts are boosted with @c-cubed vote and featured in daily posting on the @c-cubed blog. Cheers
https://discord.gg/B8JFmJ4