If I could choose a top 10 I would not have a bazillion gaming soundtrack CDs. I have a top 3.

Ys 1

Lords of Thunder

The Ninja Warriors

After that, I love so so so many old and new OST's and if I listed anymore then I'd worry about forgetting something else as so many could be tied for 4th,5th,6th and such. RPGs. Shmups. Twin sticks. Arcades.  While the OST is good but not my absolute top faves. Snatcher does hold my fave song in any game ever.

Super Mario Galaxy 2
The Legend of Zelda: Ocarina of Time
Sonic Colors
Fire Emblem Three Houses
Donkey Kong Country: Tropical Freeze
Xenoblade Chronicles X
Mega Man X
Ys VIII: Lacrimosa of Dana
F-Zero GX
Yoshi's Woolly World

I tried to limit it to 1 per series!

Mario Galaxy 1 & 2 would definitely be up there for me too, truly sublime soundtracks.

lol, yes, the final post was successful. But man it took a while and was difficult not to include other gems like: Zelda - Majora's Mask, A Link Between Worlds, A Link to the Past, Skyward Sword, Twilight Princess, Wind Waker, Hyrule Warriors, Mario - World, 3D World, Galaxy 1, Odyssey, Xenoblade - 1 and 2, Sonic - Adventure 2, Lost World, All Stars Racing Transformed, 1, 3 and Knuckles, Donkey Kong- Country 1, 2, 3, Returns, Smash Bros. Any (though that's kind of cheating)
Mega Man - X4, X2, Zero, Zero 2, 7, 2, Legends, Stella Glow, Persona Q,

That is just at the top of my head, I'm missing a bunch, but just listing these off took less than half the time as my previous post haha.

Hmm...There are a lot of individual songs that resonate strongly with me, but there's almost always several or more songs on any given game's OST that I would gladly remove if I could. Not least of all because, to maintain a theme, OSTs usually have a lot of repetition throughout - slight variations on a song which are great when paced alongside a game but less so when listened to back to back (at least for me). So, favorite OSTs (holistically) is a bit tougher category for me. Also, I'm no good at ranking them, so I'm not going to try (and, thus, the numbers that follow are meaningless).

1) Chrono Trigger

2) Xenogears

3) Chrono Cross (I'm sure you're gathering that I'm a fan of a lot of Yasunori Mitsuda's SquareSoft work)

4) Legend of Dragoon (I do still believe!)

5) Nier

6) Bastion

7) Transistor

8) Final Fantasy VII: Crisis Core

9) Pixeljunk Shooter

10) Papo & Yo

...yeah...I definitely feel more comfortable in my assessment of individual tracks :D

Thats a very good one, didnt even occur to me, but that could make my list. 

Also would have to include Xenoblade Chronicles 1 & 2. I still get chills listening to these, they ignite my emotions in a way few other video game OSTs can match.

Thought about it and this is my 4th fave OST. Only the Bday cake song sucks but everything else is a banger

Honestly, I feel like my answer can change at any moment, dependent on what kind of music I'm feeling, and what games I recently played, so I feel like I could never give a definitive answer that suits me at any given time.

With that, some of my favorite game OSTs of all time include:

VA-11 Hall-A
Deltarune
Castlevania
Crash Bandicoot: Warped
Rhythm Tengoku
Cave Story
Mega Man X
Xenoblade Chronicles
Persona 5 Royal
Persona 3 FES

There are some game music that I listen to regualary outside of playing the actual game. For most of them, picking one track as an example is difficult.

League of legends

On its way to be the best soundtrack in any game imo. Many of the different login music is just awesome. I like that a lot of the songs have singing without any words. It gives the music a better human emotional connection without using text. I use a lot of the more pumped up beats on my running playlist.

Donkey Kong Country series

No other game series come close in how much I listen to the music. The tracks works so well as background music for work. 

Chrono trigger

Not much to say. This games music is praised for a reason. Only played the game once but revisit it through the music.

Super Mario Galaxy games

Ah! Bringing a full orcestra to the Mario series. Still have one of the melodies as my wake up signal.

Starcraft

God-tier RTS game. Awesome-tier music. Beat Diablo 1 to the list.

Then there is music that is great but more to set the tone and atmosphere of the game. Without the music the game experience would be much different. That is ofcourse true for most games, but extra so for the second five.

Resident Evil 4

The sense of stress that some of the music from this gives me. Not that many actual melodies in there, but boy, do I like the music anyway. And it's not like I'm going to keep this game out of any list it can be part of.

Metroid prime

Never actually played this more than a few hours. Did play a massive amout of metroid prime pinbal for some reason though. The music alone makes me think I'm on a different planet. 

Ace Attorney series

The music quality in the games vary a lot. But it is great at enhancing the different scenes.

 
Eternal darkness

In a game where you question your own mind. This track stands out as giving your thoughts some rest. It almost sounds like history is being written. And yes, I pretty much added the game here just because of this one theme.

Halo series

Great music all around. But since I love no word vocals.

Honorble mention to the Super Smash games for collecting top tier tracks from many different series.