Britney Spears may or may not end her Las Vegas residency – she’s just not sure yet. But her two-year stint at Planet Hollywood has served as a culmination of her career so far.

Spears’ residency, at The Axis, kicked off not long after The Femme Fatale Tour wrapped up. According to early reports, the pop star would do 90-minute shows in a club-like atmosphere, for about $310,000 per night. She had been projected to earn $15 million per year for a two-year contract involving at least 50 performances.

Yet, even before Britney Spears: Piece of Me opened, the singer faced obstacles. For one, her manager had to emphasize she would be singing live – long an issue during her career. Two, low ticket sales were initially reported; however, by early 2014, Piece of Me was one of the city’s top-selling residencies.

Then, in 2015, Spears experienced an ankle injury while performing “(You Drive Me) Crazy.” Because of postponed shows, her run had been extended three more months.

Even with the longer run, Spears told E! Online at the 2015 Teen Choice Awards that she might end her residency this year to focus more on her upcoming album. If that turns out to be the case, she would last perform there on New Year’s Eve.

As Piece of Me has centered around her many huge hits, we count down her top 10 career-defining singles.

Image Courtesy of INFphoto.com

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10) “…Baby One More Time”

This track, off the album of the same title, made Spears an instant star back in the ‘90s. And, with the song’s catchiness combined with Brit’s slick dance moves in the music video, it’s easy to see why.

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9) “Oops!...I Did It Again”

15 years ago, some dismissed Spears as a one-hit wonder. While she put out moderately successful singles before this point, “Oops!...I Did It Again” opened up a second chapter for the singer.

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8) “I’m a Slave 4 U”

The song itself is nothing special, looking back on it, but her infamous VMA performance in 2001 – you know, the one with the snake – showed Spears officially grew up.

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6) “I’m Not a Girl, Not Yet a Woman”

This track stands as one of Spears’ more personal efforts, and one that foreshadowed the rest of her career. It, unfortunately, came out around the time Spears attempted acting in Crossroads, and a version is included in the movie.

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6) “Toxic”

Spears has never been a strong singer, and “Toxic” clearly indicates that. Yet, the production – those strings, that bass – makes this track memorable 10 years later.

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5) “Everytime”

Spears’ second personal effort shows her voice can be stripped down and still sound good. She won’t be able to compete with the divas anytime soon, but “Everytime” got plenty of airplay back in 2004.

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4) “Gimme More”

This track bears two distinctions. One, it’s associated with Spears trying to make a comeback after a rough, K. Fed-influenced year. Two, it gave pop culture the phrase, “It’s Britney, b--ch.”

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3) “Womanizer”

For Spears’ true comeback, this Circus track revealed she was on top of her game.

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2) “Til the World Ends”

Production wise, Britney’s songs haven’t been especially innovative. “Til The World Ends,” however, stands out, in that it has a dubstep breakdown right as the EDM style’s popularity started to grow.

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1) “I Wanna Go”

What was the last decent Britney Spears song that came out? Nothing off the supposedly personal Britney Jean is especially memorable two years later, while “Pretty Girls” didn’t have a discernible melody. So, if Spears just coasts the rest of her career, “I Wanna Go” stands as a fairly high end point. And, the video’s winking toward Spears’ past – Crossroads, paparazzi, and Mickey Mouse Club references – is worth a few views.