Any rational voter will admit that no candidate for office always tells the truth -- and that goes for presidential candidates also. This is because we have a political system that sometimes rewards candidates that tell falsehoods, and a media that does a very poor job of exposing the lies told by candidates.
But that should not be taken to mean that all candidates are the same, and tell the same amount of lies. There are candidates that lie most of the time, and candidates that tell the truth most of the time. And while I despise any lying by candidates, we need to recognize the difference between those who lie most of the time and those who tell the truth most of the time -- and reward the truth-tellers with our votes.
So, who are the biggest liars among the presidential candidates? PolitiFact examined statements made by the candidates since 2007, and it turns out that the biggest liars are three of the four leading Republican candidates -- Carson (84%), Trump (76%), and Cruz (66%). Rubio fared a bit better -- telling the truth and lying about an equal number of times. The Republicans that lied the least were Christie, Paul, and Bush -- all of whom lied about 32% of the time.
The two leading Democratic candidates did much better. Sanders and Clinton both were rated as making false statements about 28% of the time. They were also the only two candidates rated as telling the truth in a majority of their statements -- Sanders (54%) and Clinton (51%).
NOTE -- You may notice that the percentages don't add up to 100. The rest of the time the candidates were rated as making statements that were half-true. For instance, a candidate rated as telling false statements 35% and true statements 35% would have a total of lies and truths at 70%. That means he/she was telling half-truths the other 30%.