>>723757012 (OP)
This is a pretty difficult question to answer honestly. I would start first by asking what you're looking for.
>classic point and click RPG with concise pacing and storyline
Fallout 1
>huge classic RPG with tons of content and options
Fallout 2
>The Bethesda open-world exploration game they are known for making, but in a post-apoc setting
Fallout 3
>huge modern RPG with tons of content and replayability
Fallout New Vegas
>new Bethesda looter shooter and base building game
Fallout 4
It's worth noting 3 and 4 follow Bethesda's east coast storyline/setting; while 1, 2, and NV follow the original southwestern US setting/storyline. Doesn't mean you have to play them in order though.
My biased opinion: New Vegas is the best value. It's the one I return to again and again and it's great every time. Really I just like its setting, characters, and weapons/armor the most.