Despite her faults, Usagi Tsukino (aka Sailor Moon), the main character of the show, is one of the friendliest and most compassionate heroes in anime and manga. During the R season, even though Chibiusa causes the Guardians a lot of trouble and makes it clear that she has no respect for Usagi as a person or as a Guardian, Usagi constantly reaches out to her and allows herself to be viciously attacked by Rubeus to keep Chibiusa safe. She even tries to lift the spirits of an enemy (though she doesn't know it) who is actively going after Mamoru, her boyfriend and future husband.
Minako Aino (aka Sailor Venus), of whom Usagi is an Expy of. While rough around the edges and rather Hot-Blooded, Minako will help everyone, even to her own detriment (a classic example comes from Codename: Sailor V, where she helped a mangaka who was late with her job without expecting to be paid even after finding out how hard it was, and when paid didn't put up much resistance when Artemis told her to give it back). This is balanced by how ruthless she is with those who threatens her friends or mission.
Ami Mizuno (aka Sailor Mercury) is generally the most peaceful and down-to-Earth Guardian, though she isn't without her moments of Beware the Nice Ones ("Ami's First Love" being the best example).
Artemis, in contrast to Luna, is usually pretty amiable and helpful towards Minako and the others. While he does have his moments of being somewhat exasperated with Minako's antics (like Luna with Usagi), unlike Luna, he never makes any snide or blunt remarks at her expense. He becomes a Dogged Nice Guy towards Luna by the end of season 1.
Setsuna Meioh (aka Sailor Pluto) also counts, in contrast to the OuterGuardians, as she is the only Outer willing to cooperate with and help the Inner Guardians, and is very caring and warm towards Chibiusa.
Among the lesser characters, Naru Osaka and Hikaru Sorano (who only appears in Codename: Sailor V) are almost as nice as Usagi, with Hikaru being so nice that Artemis once wished she was Sailor V.
While Gurio Umino tends to be Innocently Insensitive (such as accidentally pointing out Nephrite's death to Naru), he's otherwise a pretty decent guy who eventually becomes a supporting boyfriend to Naru, even defending her from enemy attacks.
The 90s anime may have turned him into more of a JerkassSnark Knight, but Mamoru in the manga fits the bill very well. He was based on the author's idea of a dream man. He's a kind All-Loving Hero, unfailingly and unconditionally supportive of Usagi (and angsts over being massively underpowered compared to her and the Senshi, and therefore inadequate to protect her). Usagi complains that he's strict, but compared to her childish behavior he is the Reasonable Authority Figure. His first name even means "protect". In the Black Moon arc, his kindness towards Chibi-Usa and empathy with the lost and frightened little girl stands in sharp contrast against Usagi's suspicion and hostility (partially rightful, partially out of paranoia and trauma).
