Not a lot to say. I have worked as a consultant to what I consider two of the more effective UN agencies and had very good experiences with both despite the absurdly bureaucratic nature of the beast; I am still in consultant pools there and will be happy to work there again. And I had a fellowship with WEF right out of grad school, working in research.
I actually like both of these institutions to varying degrees, and both attract some wonderful, very smart people, but WEF is really full of itself, and the attendees at the events are a gang of pompous fart sniffers. If I never have to make small talk with minor Middle Eastern royalty again it will be too soon. The UN is quite a lot more humble, perhaps surprisingly.
WEF has a fucking cool headquarters, though—looks like the lair of a Bond villain (I wasn’t based there, sadly; their in-town office in Geneva where I had my cubicle is not impressive).