The Florida senator who is emerging as an establishment favorite for the Republican 2016 nomination criticized both Clinton and Trump in a wide-ranging interview with CNN's Jamie Gangel.
"To this point in the campaign, he has not proven an understanding of these issues or the preparation necessary to be the commander-in-chief of the most powerful military force in the world," Rubio said.
He also said Clinton winning the Democratic nomination over rivals Vermont Sen. Bernie Sanders and former Maryland Gov. Martin O'Malley is a foregone conclusion.
"Well, she'll be the Democratic nominee, someone who comes from a political dynasty and that, in and of itself, is going to bring fundraising capabilities and so forth," Rubio said.
He lambasted her performance in a Thursday hearing in front of the House Benghazi committee, where a Clinton email showed she'd told her family right after the 2012 attacks resulting in the deaths of four Americans that they were the work of terrorists, and not a reaction to an anti-Islam video.
"She lied about Benghazi," Rubio said. "I think it's just a little bit more insight into her unwillingness oftentimes to speak truth, in this case for political reasons."
In the interview, Rubio also demonstrated his love for 1990s-era hip-hop -- particularly West Coast rappers like Tupac Shakur.
He said lately he's a fan of electronic dance music, as well as artists who have crossed traditional lines of genre.
"In many ways it's real genius and it's a 21st-century ability to take music and use it in a way that motivates people. Some of it is blended with other sounds that are sampled from recordings that others have had in the past, and you see traditional artists being brought in and their voices used in an electronic sound track," he said.
He credited Tiesto and other DJs, and he said he listens to artists who have blended hip hop, rap, R&B and electronic dance music. He credited Canadians Drake and The Weeknd for doing that.
Rubio said some of his favorite music isn't quite suitable for children, though, because of the lyrics.
"You don't want kids at a young age exposed to lyrics that somehow glamorize a lifestyle that's art, it's not reality," Rubio said.
"So one of the issues with the '90s hip hop music is that it had lyrics that were offensive. What it actually was were people who were living in those circumstances expressing what their life was like. In the West Coast case, for example, in South Central L.A. And so it gave insight into the lives that they were living.
"But if you heard the lyrics purely without understanding that, you may think that it's glamorizing that lifestyle. To some extent it was, and so there's a difference between a 44-year-old man listening to that and a 16-year-old listening to that and not understanding the difference between artistic expression and reality."
As for his favorite movies, Rubio -- "like any guy in America," he admitted -- said he loves both Godfathers I and II. "And No. 3, I can do without."