Previous to CD quality audio (SNES, NES, Genesis, you get the idea), and not listen to any others the rest of your life, what one would it be.

Well, there are quite a few soundtracks in the days of old that still can blow me out of the water. Sonic 2 & 3, Streets of Rage, Rockman X, just to name a few...

But I'd pick Teenage Mutant Ninja Turtles 4: Turtles in Time. It was and still is simply amazing to me. It sounds fun, sounds great, and sounds so full of life. Fills me with joy every time I listen to that sweet sweet music.

Edit: LOL, typo in the title.

Probably Chrono Trigger. I still love it after all these years and, unlike some of my other potential choices, it has a lot of songs on it.