Best 2 hour RPG
Best 10 session RPG
I'm behind, but this is a perfect twofer. I play a lot of D&D, so there is my answer. Only 2 hours, grab some premades, an AL mod (or roll your own), and get to playing. 10 sessions is a bit vague, 20-60 hours, but you can run an arc in 3 sessions, making 3 arcs and an epilogue; perfect for any story!
RPGs are what you make them, so my experiences with D&D may not be the same as everyone elses, but whatever your favorite RPG is I'm sure you can do the same with that. Tomorrow's question is less vague, so I'll be back with a few links for you to follow.