I tend to overthink "favorite" questions. I tend to tie myself into pretzels trying to answer them, to come up with some kind of objectively and permanently "correct" answer, as if such a thing were even possible. But instead of doing that this time, I am going to go with what my heart is saying (screaming!) right this moment:
Sonic 3 & Knuckles.
You see, my sister was my best friend growing up. Pretty much any time I wasn't on the computer (and some of the times I was), I was hanging out with her. It wasn't that I didn't have other friends; it was that she was my favorite person in the whole world, even if (regrettably) I didn't always act like it.
For reasons I don't wanna go into right now, our family didn't have a lot in terms of video games. We had a NES, I personally had a Game Boy and Game Gear, and then we had our computer. Now, of course, I had played SNES and Genesis games (in fact, I sought out and savored every possible opportunity to do so), including the 16-bit Sonic games right around when they first came out. (Hell, I even got to play one of them before it came out, but I'll save that story for another time.) But actually owning a 16-bit Sonic game was just out of the question, or so I thought.
Then, one day, in like 1998 or so, I was puttering around the Internet and found demos of Sonic games for the PC. The one that intrigued me most was the Sonic CD demo, but I also checked out the one for the Sonic & Knuckles Collection. This was a PC game that included Sonic 3 and Sonic & Knuckles, in all their locked-on and non-locked-on permutations, plus the full Blue Sphere minigame. It could output either Adlib or General MIDI music, but otherwise seemed completely identical to what I remembered of the Genesis version, which I thought was amazing.
The demo only included Angel Island Zone, but that was enough for my sister and me for several months. Usually, we did the pseudo-co-op thing (I played Sonic, and she played Tails), and sometimes, she played as Tails by herself. We both scoured every square inch of Angel Island, and learned the first four special stages. We put so, so many hours into this demo. So, naturally, I asked for the full game for my sixteenth birthday, and got it. Not only did we have an absolute blast exploring the full game, but we played the Competition mode excessively (she literally always beat me at Balloon Park). It was our favorite game, by far!
(Side note: if you know much about S3&K, you know that the PC version had some different music, most notably in the last three zones of Sonic 3. I didn't know this at the time, so the PC tracks were the ones I heard first, and the ones I'd later become nostalgic for. So, when I first played Sonic 3 on the Genesis, and got to Carnival Night Zone, I had the exact same "GAH WHAT THE HELL IS THIS" reaction that I'm sure Genesis players had to the PC music. I had to listen for years to people saying that my preferred version of the soundtrack was "wrong" and "not the REAL music" even though, in my opinion, the PC songs fit classic Sonic better. You wouldn't believe the vindication I felt when the community discovered that, actually, the PC songs were prototype songs, and were therefore the original tunes all along!)
So, time passed, we grew up and grew apart, and I finally got the courage to come out at age twenty-nine. (I wish I had done it much sooner, but my parents were fundies and I had to deprogram from that, sooooo yeah.) Most of my family just rejected me outright. But not my sister. Don't get me wrong; she still was (and is) a fundiegelical. But she felt that there was no sense in being a dick to me about my transness, and therefore made good-faith efforts not to deadname or misgender me.
In fact, she went even further than that. I remember, several years back, when she and her husband and son were visiting my town, and I trepidatiously agreed to meet up with them. Upon seeing me for the first time, my nephew asked me what my name was, and I told him truthfully, "My name is Alyssa." And my sister was like, "Can you say Alyssa?" Just. Wow. Wow. We've talked a few times since then, and I wish we could talk more. I also wish she was more accepting, yes, but I truly think that she is doing the best she can within the mind prison she's in. And I treasure that.
So, yeah. I play it because it reminds me of her, and I like that. Specifically, I still play the PC port (albeit with Sega PC Reloaded and the S&KC Mod Loader), because every little detail of that port is seared into my mind and heart. And I don't just mean the music; I mean, all the little inaccuracies. The jittery special stages. The slightly mistimed credits. The way the pallette gets all fucky in that orb bonus stage. Sound effects playing when they shouldn't. I even went as far as to use MainMemory's music config program to make the game use my old sound card's soundfont for MIDI playback, just because that's what reminds me most of the time we spent playing this game.
And it doesn't hurt that S3&K is, like, super glorious just as a game. All the characters are fun, there are so many levels (and most of them are great with fun gimmicks), the music (no matter which music or how you enjoy it) is exquisite, and idk, I just love Sonic!! Pretty much the only thing I don't like about S3&K is that last Hyper Sonic fight, which I find clunky and awkward. The rest is magical. <3