This one shall be fun, as opinions tend to vary, and usually comes down to a debate on which style you like (though honestly, there is no longer a debate in my book

)
Let's meet our contenders ladies and gentlemen
Super Mario RPG

The original.
Paper Mario

The spiritual successor.
Mario and Luigi: Superstar Saga
Paper Mario: The Thousand Year Door

The Paper-crafted sequel.
Mario and Luigi: Partners in Time
Who let the babies out, woof woof
Mario and Luigi: Bowser's Inside Story

Did someone page the King of Awesome?
So there we have it, I will note that Super Paper Mario didn't make the cut as the RPG to platform ratio is vastly different than in any other game in the series.
So let's hear it, which is the best of the best, the cream of the crop, the one to rule em all?