If it’s Rubio, I predict he’ll own a 60% rating around the time of the convention. This isn’t a crazy prediction. John McCain got over that and stayed there or near there until the financial crisis and his rather odd reaction to it killed his candidacy dead:
http://www.pollingreport.com/l.htm#McCain
Kasich can probably get to about 55%, and Paul probably too. Some of the other guys can probably hit 50-52%. Some of them never will, namely Scott Walker, Jeb Bush, or Rick Santorum.