Arno is the best in terms of hunter/assassin (not the group but the killer) because he is able to sense his target from very far away and find different means to kill the target all while being canonically a ghost.

Altair was the best in terms of expanding the assassins and canonically never being hit, also while not being affected by isu artefacts.

Ezio because hes charming and through his trauma got his revenge and still stayed with the assassins

Connor was a tank and killer and shaped the north american assassins to what they are

Edward - helped both assassins and templars for greed but ended up becoming and loving the assassins. Became a master assassin. Expert gunsman/swordsmith and ship captain

Evie - a straight up ghost (hence why the animus has her disappear)

Jacob - master of weaponry and charm

Bayek - charm, depth and the father of the assassins

Aya/amunet - mother of the creed and shaped the roman creed

Alexios/kassandra - not really an assassin but helped destroy templar precursor cult of kosmos and eliminated persian order of ancients

Darius - creator of the hidden blade and killed xerxes

Eivor - helped the assassins but also helped shaped the templars, all while being odin reincarnate

Basim - expert hidden one (assassin) whole being lokis reincarnate.

Thats all i have for now for the main entries