Sanders - enjoys the most positive favorable rating,tops all 3

http://www.cnn.com/2016/03/01/politics/donald-trump-hillary-clinton-bernie-sanders-poll/index.html

(Snip)
In the scenario that appears most likely to emerge from the primary contests, Clinton tops Trump 52% to 44% among registered voters. That result has tilted in Clinton's favor since the last CNN/ORC Poll on the match-up in January.

But when the former secretary of state faces off with either of the other two top Republicans, things are much tighter and roughly the same as they were in January. Clinton trails against Rubio, with 50% choosing the Florida senator compared to 47% for Clinton, identical to the results in January. Against Cruz, Clinton holds 48% to his 49%, a slight tightening from a 3-point race in January to a 1-point match-up now.

Sanders -- who enjoys the most positive favorable rating of any presidential candidate in the field, according to the poll -- tops all three Republicans by wide margins: 57% to 40% against Cruz, 55% to 43% against Trump, and 53% to 45% against Rubio. Sanders fares better than Clinton in each match-up among men, younger voters and independents.

(snip)
As noted above, Sanders holds the most positive favorability rating of any of the top candidates for president: 60% of registered voters view him positively, 33% negatively. He is the only candidate seen favorably by a majority of voters, and one of four who are seen more positively than negatively.