Daytona USA - it's one of my favorite games ever. So i have the Original USA Saturn version, the JP Saturn Version, JP Championship Edition Saturn and the DC one.
Because it's one of my favorite games and because.. well it's Daytona.
Outrun - I have it on the SMS (Tectoy Version) bought it new. Saturn version (Sega AGES collection) got it as a gift. Outrun is a personal favorite, and i would love to own all the versions, but it's impossible, there are too many.
Phantasy Star I - SMS and Saturn versions, because i wanted to play with the FM soundtrack, so i bought the Saturn version.
Also, i've heard there's a non-black (grey) version of Killer Instinct, so i'm trying to hunt that down too... because if i once spend 12 hours direct, playing KI, i can say that i like it.
I sold most of these in the great purge of 2015.
Most of them were collecting dust anyway.
In fact, i don't think i own duplicate copies of any game at this point.
I only kept my SMS and Saturn games, but i sold all Daytonas except for the JP Saturn version.
And i sold the PS1 and outrun saturn, because mega-money.
Funny to look back to it.