Any comprehensive pack should start with the foundation of the Genesis library. Many of these were originally "pack-in" games sold with the console: Golden Axe Golden Axe was a Sega Genesis game. Golden Axe Sonic the Hedgehog 3
Disclaimer: This guide is for educational and preservation purposes. Ensure you own the original physical media before acquiring ROM backups. roms sega genesis pack
When looking for a pack, decide which tier fits your needs to avoid downloading 50GB of data you won't use. Any comprehensive pack should start with the foundation