It's a pity WRC has had loads of problems recently, because I personally believe rally drivers are probably the best in the world. It is hard to make a comparison between different forms of racing, but when you consider the great number of surfaces/conditions rally drivers race on or in, plus the fact that unlike a traditional track, you can't memorise the corners...yeah. Just look at how much Kimi Raikkonen struggled in rallying.
There have been many great drivers over the years in rallying I wouldn't hesitate as claiming as one of the best of all time. But for me, Sebastien Loeb is the best driver in the world right now. It's not just the 9 WRC titles he has won, but how diverse he has been. He has made a smooth transition to circuit racing and is improving all the time, he's smashed the Pikes Peak record, he's raced at Le Mans and finished on the podium, won a gold medal in the X Games RallyCross. Just a pity he never got a super license - would've loved to see him race in F1.
I think for Formula One drivers to be claimed as "the best in the world" they have to show that diversity. In the old days, Jim Clark or whoever would be racing in F1, F2, touring cars, sports cars, racing at Indianapolis, and he was always competitive/winning. I'd just love to see that these days. It is just unfortunate that we have so many F1 races and teams are scared of their drivers getting hurt in another form of racing that we don't get to see it. But for me, that is why I'd never claim that all 22 F1 drivers are the best in the world, because why on earth would you put someone like Max Chilton above Sebastien Loeb, or Tom Kristensen? Anyone with any sense just wouldn't.