Fangraphs is a lot more user-friendly as they have a more comprehensive glossary and allow for easier comparisons that can be customized. I think B-R can do that, but only if you pay and since I don't, I do not know how good it gets.
But with defensive numbers, Fangraphs is better because they can be tabulated over multiple years more easily. The single year numbers on B-R don't really tell anything, because a good defensive evaluation shouldn't be based on a single year if you want an overall picture of a player.
Of course, even then, WAR numbers represent accomplishments and not ability. So there are always other factors that can influence them that cannot be accounted for no matter what, like the ability of the guy standing next to you...