TOS: Sulu
I don't really relate strongly to anyone on TOS, but Sulu has a certain aspect of enthusiasm for the things he loves that's pretty relatable to me even though his specific interests aren't mine. And his general manner of interacting with people and life is generally open with friends and professional at work without being as aggressive or dramatic as a lot of the other characters are, which feels way more comfortable to me.
TNG: Dr. Pulaski
This is again a show where I don't really personally relate to anyone that much, but Pulaski at least has a certain amount of down to earth attitude combined with a genuine curiosity for curiosity's sake that I can see myself in her a bit.
DS9: Ezri Dax
This is the show that really feels relatable to me overall. I could've chosen at least 3 or 4 different characters here, maybe more, but Ezri definitely tops the list. She really has that sense of feeling a little uncertain, a little out of your depth. Feeling like you're surrounded by people who are way better at stuff than you, even though you certainly aren't stupid or incompetent. There's a really relatable amount of struggle there without it ever feeling over the top or artificial.
Voy: Seven of Nine
Seven has some similar elements to Ezri with the uncertainty and feeling out of place some times, but in addition to that she also adds this layer of an affinity for rules and systems. Not in the sense of everything needing to go according to the rules, necessarily, but in the sense that's it's just nicer and less stressful when you know what to expect because you know how things are supposed to work. And she also adds a much bigger element of family and the push and pull of that in her relationship with Janeway.
Ent: Hoshi Sato
Hoshi fits pretty neatly into the same row as the last two in terms of uncertainty and a certain amount of confidence issues. She also adds the linguist element, which is something I find really interesting, too.
DSC: Saru
And again Saru is a character with some confidence issues and uncertainty plus a bit of a preference for things to go according to the rules, and a more or less understated manner of interacting with people. Which at this point is starting to sound like that's all I think I am, but really it's just that I don't really see the other sides of me much in any of the characters from any of the series. At the end of the day, Star Trek is often adventure centric and most of the characters are typically drawn as heroes and adventurers first which just isn't something I identify with.
PIC: Riker
This one was another show that I couldn't really relate to anyone. It has Seven, but Annika Hansen decades after Voyager doesn't really feel relatable to me at all anymore (still a great character). And I could see maybe some aspects of myself in Dahj/Soji but the whole aspect of big family secrets and an almost ordained destiny puts the character way too far away for me. If forced, I guess I'll have to take Riker here, who I never related to at all in TNG, but his role in PIC is a lot more about family and the whole sort of peacemaker role, balancing loyalty between different people. That is something that's a lot more relatable to me.
LDS: This one I honestly can't really answer properly. I've seen the show, but it didn't pull me in deeply and I had a tendency to get distracted or walk in and out. Bottom line is I barely remember most of it. I can say with certainty I don't relate at all to Boimler or Mariner, nor any of the secondary characters I can remember. I guess I would have to choose either Tendi or Rutherford, but I don't remember them that well. I think Tendi felt more like a generally relatable character overall, so maybe her. But I feel like there was also an element of over the top bubbliness and extroversion there and maybe some willingness to believe really weird things so it doesn't really feel like a satisfying answer, either.
Overall: I never would have expected this off the top of my head, but after thinking all of them through I have to give the overall spot to Seven of Nine as the best balance of the most relatable elements.