Meaning of The best is incomplete without a context. If we consider the best to look at, then mankind is the best.
Allah says in 95:4 -
Verily We created man (al-insān: the generic) in the best of forms,
[in the best] proportioning of his shape.
(Al Jalalain Tafsir). It tells us that mankind is the most spectacular in sight.
But we must not forget the Jinns. The Jinns were created from scorching fire. So they are as miraculous as humans.
Regarding The Best of the Creatures, Allah says in 98:7
Truly those who believe and perform righteous deeds — they are the
best of creatures (al-bariyya means al- khalīqa)
(Al Jalalain Tafsir). This gives the answer to the header of the question. A Jinn or a Man, whoever does righteous deeds is included in the best of the creatures.
In Al Jalalin Tafsir, verse 17:70 is explained as such:
verily We have honoured, We have preferred, the Children of Adam,
[above other creation], by [giving them] knowledge, speech and [their
being] a creation of even proportions amongst other things, including
their [means of] purification after death, and carried them over land,
on animal-back, and sea, in ships, and provided them with good things
and We have preferred them above many of those whom We created, such
as livestock and wild animals, with a marked preferment. (the min has
the sense of mā, ‘of what’, or something close to it, and includes the
angels, the purpose being to give preference to the [angelic] genus;
there is no requirement to give [explicit] preference to the
individuals [of this category of being], since they [angels] are
superior to mankind, excepting the prophets).
So we cannot simply conclude there are better creatures than Us, nor can we say We are the best . The Angels, the Prophets, and the group of individuals among Man and Jinns combined who do righteousness and obey God are collectively the Best of the Creatures.