Neither. Both have gone horribly downhill.
Fortune is prestigious in that has lots of ads for expensive toys. But its business reporting – which used to be pretty good – has evolved into lots of feature stories about the rich and famous, and minimal if any business related journalism or serious reporting.
Newsweek, when it was owned by the Washington Post (and even before that with the previous owners) was a good, hard hitting, break-the-news sort of publication. They were bought and sold a couple times, fired practically everybody, and now, they are not really into investigative journalism like they used to be. TO a degree, they also have gotten out of the real news business and just print features.
If you are interested in reading one of these magazines for news, they both suck.
If “prestige” means pretty pictures and ads for expensive cars, then Fortune is the choice.
Neither of them are a shadow of what they used to be.