UPDATE: Britney Spears' 'Baby One More Time' won in Round 1! Vote for 'Baby One More Time' in Round 2 of the competition here.

Welcome to March Music Madness! Here at PopCrush, we've selected 32 of the most iconic pop songs released from the '80s to today (divided into brackets by decade) -- and now it's your job to vote and decide which song will be named the Greatest Pop Song of the Modern Era. May the best song win!

The Spice Girls took the pop music world by storm with 'Wannabe' in 1996, and Britney Spears shook its core once again with 'Baby One More Time' in 1998. Both acts were confident, fun, sexy and cute all at once, with one bringing us an unforgettable girl power anthem in the mid '90s and the other giving us a welcome return to straight-up pop goodness in the late '90s. Is 'Wannabe' or 'Baby One More Time' a more deserving choice to be named the Greatest Pop Song of the Modern Era?

'Wannabe' was the Spice Girls' only single to hit No. 1 in the U.S., but it became the best-selling single by a female group worldwide. As the story goes, the girls' record label actually pushed back on releasing 'Wannabe' as their first single, with Geri Halliwell (aka Ginger/Sexy Spice, pictured above) reportedly saying, "It's not negotiable as far as we're concerned. 'Wannabe' is our first single." It's a good thing that those label execs listened to her, since the fun, pure dance-pop track turned into a sensation, even winning an Ivor Novello Award and a BRIT Award in 1997.

'Baby One More Time,' released two years after pop music fans latched onto 'Wannabe,' introduced the soon-to-be superstar Britney Spears. Coupled with a slightly controversial music video (at the time), in which Britney sang and danced around in that impossible-to-forget school girl outfit, 'Baby One More Time' propelled a career and turned its singer into a pop culture icon. The song made it to No. 1 across the globe, was seen on 'TRL' daily, was nominated for a Grammy and won both a Teen Choice Award and an MTV Europe Music Award.

Should 'Wannabe' or 'Baby One More Time' make it into the next round of our Greatest Pop Song of the Modern Era bracket? Think carefully, choose a song and vote until the polls close for this round at 12PM on March 11. You can vote up to once an hour, so keep at it to make your voice heard!