That's a mean question since the RPG genre is so big.
I can split it up a bit:
In regards to story: Tales of the Abyss
Gameplay-wise: Tales of Graces F/FF12
Best graphics: FF13
Best battles: Tales of Symphonia/TotA
Best OST: FF13
Most fun: Brave Frontier (yes, people)
Most diversity: Borderlands 1+2 (It's an FPSRPG)
Most grinding: Star Ocean
Most nostalgic: Pokemon G/S
The hardest: FF10
What is in your opinion the best RPG of all time?Please don't judge by graphics since in most games these days the graphics are better than the gameplay.Games like Icewind Dale had long and good gameplay butdidn't have good graphics.
As for my opinion,i will go with....Dragon Age Origins