Credit the mass proliferation of smartphones, the breakaway success of shows like Serial and NPR's Fresh Air, or the retro radio quality of the format , but Americans are now more obsessed with podcasts than ever. More than 57 million Americans now listen to at least one podcast per month, according to Edison Research, with the total number of those tuning in up 75 percent since 2013.

There are literally tens of thousands of different podcasts, all focused on a specific niche topic, now available on iTunes and other listening apps. After tuning into several of them, I've honed in on the six that I personally subscribe to and consider to be "required listening" during those extra pockets of time that crop up in my day.

After all, if I have to sit through a subway delay or encounter an epic line at the DMV, I might as well be getting a little savvier about my business--and the world--while I'm at it.

1. Planet Money

NPR's podcasts always top the charts, largely because they've mastered the art of "eat your vegetables" listening. NPR's Planet Money manages to make the vegetables of learning about the economy taste delicious, and breaks down small parts of the economy into entertaining episodes twice each week.

2. StartUp

If your new business idea is anywhere from a glimmer in your eye to fully incorporated, subscribe to Startup with Alex Blumberg. The first two seasons of this podcast follow founders of a startup as they get their business off the ground, while episodes in the third season follow different companies embarking on a big change in their business.

3. Coffee Break With NYWICI (New York Women in Communications)

Every super-successful woman in media has an equally compelling story to share about how she got her start and what she's learned on her journey to the top. On Coffee Break with NYWICI, Julie Hochheiser Ilkovich (my fellow Masthead Media co-founder) chats with these iconic women about a broad range of career-related topics, including mastering the job interview, managing up, personal finances, entrepreneurship, and time management.

4. The Tim Ferriss Show

Tim Ferriss's bestseller The 4-Hour Workweek is practically the bible for those who believe in working smarter, not harder--and has some fascinating ideas for those of us who believe in working both smarter and harder. The Tim Ferriss Show podcast interviews people who are at the tops of a diverse range of fields (think Malcolm Gladwell one week and Arnold Schwarzenegger the next) to get insight on the routines, tactics, and habits that make them so successful.

5. Politics and More

The past few months have given many of us a politics overdose, but when you're ready to ease your way back tune into The New Yorker's Politics and More (formerly called Political Scene). The New Yorker executive editor Dorothy Wickenden leads this liberal-leaning political discussion with New Yorker writers, and engages in intelligent debates - not yell fests - during each 20-minute episode.

6. The Jay & Farhad Show

CNBC executive editor Jay Yarow and New York Times "State of the Art" columnist Farhad Manjoo dig into tech stories on The Jay & Farhad Show. From reviewing Apple's latest products to explaining self-driving cars to dishing on whatever discovery Elon Musk has made this week, this podcast will keep you up to date on the latest in tech.