Elim Garak, because how can you not love a ~~patently duplicitous and yet still somehow generally benevolent smooth-talker who chews all the scenery and exudes the queerest energy~~ simple tailor?

Janeway for me. She expresses anger in the right way and she sways her enemies with forgiveness. And she's a scientist.

It's a basic ass answer but Sisko. Star Trek has tried moral compromise a lot by now, but Sisko remains the only one where it really hit for me. Later Trek, where it's more common, just doesn't have the same level of professionalism or idealism for it to feel meaningful.

Garak

It's a tie between Mariner and Burnham.

Odo. Hmph.

Dukat. I don't like him a person, but he's a great character. No other Trek character has ever been written as richly or layeredly as he.

At first you assume he's your basic racist bent on hatred and power. Then you realize his obsession with Kira isn't just about destroying an enemy, but his secret love-hate for Bajoran women. We meet Ziyal whom he mostly loves, but is ashamed of. He goes mad, starts a cult, makes himself appear Bajoran and starts a relationship with Kai Winn (ostensibly with other motives, but I think he reveled in it), and ultimately dies for and in his mad faith.

DS9 is lower on my list when I rank the various series, but some of the characters, and defininitely Dukat, top the list of characters.

The crystalline entity, because it's pretty.

Spock.

The why should be obvious, but this video goes some way to explaining it.

Janeway is still my Captain.

But they have so many good characters in New world and lower decks... The new feeling and energy is so refreshing.

First, I love characters that are regularly puzzled by human beings / being human:
Spock
Data
Odo
The Doctor
Seven of Nine
Saru

Second, I love strong female characters:
Katherine Pulaski
Kira Nerys
Kathryn Janeway!!!
SNW Uhura
SNW Chapel

Third, I love queer characters:
Guinan
Garak
Jadzia Dax
Adira and Gray

I might have forgotten an awfull lot of equally amiable characters, which doesn't mean that I don't love them.

Chewingbacca. His laser sword was the best and he had nice eyes.