With all of the RPGs on the market, there is definitely no one 'best' RPG out there. There are two schools of thought. Either the most commercially successful is the best, or the more people a game pleases the better it is. Either way you look at it, when it comes to a successful RPG they typically have a great story, good playability, and good overall appearance.
Story is nice when it comes to RPGs. A great story will have a solid and unique plot line. It needs to be original and immerse the player into the story. Modern games are typically open vs. linear and there is usually more than one way for the game to end.
In a well-built story, there will also be loads of content for the player to explore. Usually it will have a lot of quests for the main character or party to take on. There will be a large amount of items in the game that you can collect, as well as lots of cities and locations to visit. There should also be a wide variety of character choices for the player to make, including visual customization.
The second most important aspect of a good RPG is playability. There should be good game balance with the difficulty levels. The game should be easy enough for most player to finish, but hard enough to give most players a real challenge. The rules in the game should be lightweight enough to not hide down the game, but comprehensive enough to give the game the effect it desires to bring along.
The price of the game can be an aspect of playability too. If the game costs a lot more than average games for its market, then are many people going to be able to buy it? Also, if the game requires an extremely high-end PC then many players may not be able to play it without upgrading their systems.
The third most important aspect and often the first a player notices is the visual appearance of the game. Are the graphics modern? Does the artwork have an appearance that the game will be able to move forward into further editions of the game? Or will they have to completely revamp the graphics and artwork? And are the graphics efficient enough to be good looking but not tax the system running it too much?
There are a lot of different factors that come into play when trying to judge the best RPG games for PC or console gaming. Story, playability and appearance are three of the main factors when judging the best RPGs out there. In the end though, it is a choice that each individual player has to make.