I'm obsessed with Kirk/Spock slash fiction, TOS Spirk is my OTP. I also prefer Kirk centered stories (slash and nonslash) where he struggles, gets captured, shot at, ect. cause I like how Spock gets all Vulcany for him (but mostly pure whumpage). I also really like stories that are of the triumvirate because McCoy is an intricate part of the Kirk/Spock relationship and he deserves to be included more in the Spirk stories. Either as the platonic best friend or a lover because it's very clear that McCoy cares about Spock and Jim, and to Spock and Jim McCoy is more than just a doctor and crewmate, he's family.
I read some AOS/Kelvin Timeline stories but there are few things that annoy me when some ff writers have the habit to categorize their work in the original series or write original series stories and change kirks eye color. When I'm reading a classic TOS I want the beautiful hazel Shatner eyes! I also don't understand why the need for excessive explicitives is necessary in the AOS/Kelvin Timeline stories, I've seen the movies and they do not swear every other word. It's so out of character and its irritating. As far as pairings go in the AOS/Kelvin Timeline the only one that really makes sense to me is AOS McKirk. I indulge in AOS Spirk sometimes because there are really great fics that make the pairing believable but TOS Spirk is my true love.
Besides the obvious first ever slash pairing, I really like the profund philospy that makes Star Trek, the need for adventure, the love and compassion for others, acceptence of all races colors, species, orientation, creeds and so on, uniting as one to spend our energies on scientific discovery instead of war greed and hatred. I strongly hope that the Star Trek 23rd century way of life can become a reality for us someday in the 21st century =]