1. Anonymous "insiders", Politico
2. The Fix team, Washington Post
3. Ian Leslie, New Statesman
4. Betting markets (in this case, PredictIt)
As faith fell in polling – thanks in part to a surprise Conservative majority win in the UK's 2015 election – betting markets became a more popular way to try to predict the future. But their record has been hit and miss, as this January 2016 piece from The Economist shows:
"At the time of writing, PredictIt reckons that the fight for the Republican nomination is between Ted Cruz and Marco Rubio, and that Hillary Clinton has a 54% chance of becoming the next president."