I'm gonna go with SMB1.
I was a kid when the original released and I'd beaten it a hundred times because, for a while, it was the only game I had. To be honest, I didn't really like it. It was too simple for me.
When I got All-Stars, it felt like a new game. It felt like a good game! Yeah, it was just a graphical overhaul but everything felt exciting and new. SMB2 and SMB3 were already fun to me (with 3 being the best game ever). Finally, SMB1 felt like it belonged.
Lost levels? Beat that one once and swore never to play it, again.