I know, kind of a cliche question, but I’m genuinely curious! Also, I’m very new here, so I want to get to know you guys on this site a little bit.
For me, I liked English, simply because the information just…came to me naturally.
My favorite subjects were English and history. I loved reading and writing, so it was no surprise I liked English. I’ve always viewed history as a complex chain of stories, so I guess there’s an overlap there. I went on to teach both subjects.
Mine was Algebra. Word problems especially. But when it came to Geometry…I couldn’t stand it, and I dropped the class. 
Creative Writing. Like English, minus the boring books by dead white people. I got to rant at the world, for once.
Then I discovered the Straight Dope and realized I could do the same thing here without having to pay some dude in a suit a bazillion dollars in tuition.
I actually had three: Math, Art and Music.
Both of my parents were artists, so art came to me naturally (I never had to “learn” to draw). I excelled in music, and was the concertmaster of my high school orchestra. And I was always the “teacher’s pet” in math class, always knowing the correct answer to any problem.
English and history.
I was lucky enough to have an English teacher who recognized my love of literature and writing, and encouraged it. I eventually became a professional writer. As for history, I had a teacher who blew the dust off those creaky old kings and rulers and wars and dates, and showed us how what happened in the past affects us today. It was fascinating.
I should add music. I learned piano as a child, and played trombone in the high school band, and all those lessons prepared me to learn instruments myself. I am most at home on the flute nowadays, even going so far as to study classical flute with a private teacher, though I’ve played with plenty of bar bands whose idea of classical music is Led Zeppelin. (And yes, I know the opening of “Stairway to Heaven,” having played it so often.)
How did he or she do that?
In high school, it was foreign language. I took French and Spanish, and I planned to learn more in college and become a language teacher. I found the vocabulary and grammar rules to be a fun puzzle to decode. To this day, I love languages and figuring out how they work. But instead of teaching, I had a career in, then working for, the U. S. Navy on the aviation side. The languages came in handy on deployments.
It varied. Throughout k-12 I was all about any science class. It changed as I got older. Every semester in college, there was at least one teacher whose class I looked forward to. A good, engaged teacher makes all the difference.
In community college I had an English teacher that got me into writing a bit. Later, I moved to Tennessee and took some history classes to finish a degree. The teacher was an old southern gentleman who used to take the most outlandish positions, then somehow applied it to a history lesson. That guy was a gem. I had to take an elective, so I took Children’s Lit and even that was a great learning experience, since I wasn’t exposed to much of that when I was young.
Later in life I developed an interest in languages, something I wish I had when I had access to free language lessons in public school. I did not fully avail myself of them. After a year of German classes, I signed up for German 2, and wrote, “German 3” on my notebook. Yeah, I wasn’t a good HS student. 
I swear, it’s like my brain wasn’t fully baked until my 20’s.
Geography and biology.
Drawing. I did artistic drawing until 8th grade, and technical drawing in high school.
I loved doing them both and I got only maximum grades.
I enjoyed English in college so much that I lied to register for a class taught by Christopher Rawson.
It was an upper level course offered to English majors only. I registered and Rawson found out halfway through the semester that I was a biochemistry major when he stopped me after class to ask what English courses I had lined up for the next semester and offered to mentor me.
Regular math (algebra etc.) was not my strong suit. However, I did like high school geometry. What I recall most is “proofs” - the step by step logic of proving a hypothesis. It was a like solving a puzzle and required some insight. My teacher, Mrs. Fish (viewed by most as a battle-axe of sorts and widely feared), was my favorite.
Depends on what grade I was in. I loved reading time in 4th grade. By the time I hit high school, I really like algebra (but NOT geometry) and chemistry.
I loved science class in grade school.
All through high school I hated pretty much every class. And then I took physics my senior year and loved it. Finally, a subject that relies more on understanding than memorization. It also helped that the teacher was really good. He was a retired Air Force Colonel, and genuinely enthusiastic on the subject matter.
English and history.
I used to love to write essays and short stories so I really liked English. I liked history because I loved learning about the the times and people before us.
Edit: I also loved art class, but quit that in the 9th grade. My dad insisted I’d end up poor in life if I continued. I was really good, too, at drawing.
I know this wasn’t directed toward me, but I strongly believe all history teachers should do this. My approach (and a common approach today) was to teach history thematically instead of just chronologically. That meant taking a topic: racism, military actions, economics, immigration, etc. and examining it chronologically. I’d start with today and then we’d look into how that situation developed up to the present day. We also spent a little time each day watching/reading the news. Then when something like Fergusson happened, I’d ask students how that situation was similar to and different from the 1965 and 1992 L.A. riots. What were the underlying issues? What was the inciting incident? Why are we still dealing with those same issues today?
Sometimes my students thought it was weird that we’d just been covering a certain event, and here was a news story that related to it. Of course, it wasn’t weird at all. The more you know about the past, the more connections you see with the present.
Literature especially, and history to some extent. I’m currently pursuing a BS in civil engineering. My “arts” requirement for the general education component of my degree was fulfilled by an American Literature course, which remains the most enjoyable course I ever took. Go figure.
Math nerd here. I loved every math class I had, from jr. high to college. I lost the ability to keep up when I hit Green’s Theorem in 3rd year Calculus. That was the point where I just didn’t get it any longer, and that was the end of my math education. I still love the stuff! Three cheers for Roger Penrose’s Nobel Prize! A salute to Karl Gauss!
My next fave was Geography. I got pretty good at naming countries and finding them on a map.
Welcome to the Dope, Baleaf_1997!
I like almost any class I took in school, but the most significant had to be computers in my senior year of high school. This was 1968-1969. Though we learned Fortran (about two weeks after the teacher did) we never got to actually run any Fortran programs. We did run programs on our LGP21 which was the transistorized update of the LGP30, from 1962, with 4K of rotating memory, one accumulator, no assembler, and not much else.
I spent hours after school programming it, and wrote an assembler for it from scratch. It made me want to major in computer science. In grad school I wrote an emulator for it in Lockheed Sue microcode, and I saw from my Google search that someone implemented in in an FPGA.
There is an LGP30 in the Computer History Museum in Mountain View.
The class that changed my life.