I could go to town ranting and raving over the Sonic series OST's. But the first 4 are my absolute faves by far. Sonic 2 is my top GOAT, but closely followed by Sonic & Knuckles. The colors, speed, sound, and attitude was why as a kid I saved for a Genesis over a SNES. Plus many friends had the SNES so I wasn't missing out when hanging out or spending the night.
I've been on a Genesis kick lately, hell I actually never stopped. Got 'em all on my Sony Walkman mp3 player. Plus the shooters had great OST's, hell the whole system was full of great music. Some I've been enjoying lately but made an immediate impression way back when.
I appreciate seeing the GG and Master System versions too. Great conversions. Sega was really on to something at this time. The whole package was awesome, beautiful artwork in a world I wanted to run around in, a game you could beat in a sitting but wanted to replay, fantastic music that packed some serious groove. There were a few on the GBA that I enjoyed but not to the same extent of the Genesis titles. I really enjoyed the two SA titles on the Dreamcast, still have 'em, but they never approached the greatness of originals for me.