Vegas Bookies predictions to be the most accurate, probably because they make (or lose) money based on their objectivity.
Bookmakers don't make predictions.
Bookmakers frame pay-out odds on the basis of the weight of money bet on each particular outcome in such a way that they secure their margin no matter who wins because the total probability weighted pay-out is less than the amount of money bet.
The odds pay-out converted to probabilities is less than 1 however we know with a probability of 1 that one of the jockeys will ride to victory on the Pegasus of democracy.
I guess you mean that the amount of money bet on a certain candidate ( as reflected in the odds on offer ) is a reasonable guide as to how the population in general will vote.