I think Kelly has seen more success. Avril didn't have the longevity.

Avril was the precursor, I'll admit.

But Kelly took it further, went bigger, and lasted longer. Kelly's also proved to be more diverse.

Avril
Bigger albums
Bigger singles
Bigger net worth.

This.
Avril's peak was slightly bigger, but it was short-lived.

Avril's bigger in a lot of countries outside the US (mostly Japan) but Kelly is definitely bigger in the US.

Avril

Kelly is a one album wonder

Avril obviously, Kelly only had one big album whereas Avril had 3.

Um, what?
-Thankful was #1, sold 4.5 million copies, had two hit singles.
-Breakaway has sold 13 million, had 5 hit singles and won 2 Grammys.
-My December didn't have any shot at succeeding due to her record label sabotaging/pulling it, and it still sold 2 million WW and had a hit single.
-All I Ever Wanted was #1, has sold about 2 million and had 2 hit singles.
-Stronger has sold about 2 million, had 2 hit singles and won a Grammy.
-Wrapped In Red has sold about 1.5 million and was the best selling holiday album of 2013, outselling a lot of Pop girl's new releases at the time in a matter of weeks.
-Piece By Piece hasn't done amazingly, but it was #1, had a hit single/big tour, and is nominated for a Grammy.

She's only had one HUGELY successful album, but has had plenty of success otherwise. Far from a "one album wonder".

Like I said, a one album wonder. Everything else after and before Breakaway were underwhelming especially considering the time of most of the releases

Her album sales for the most part are mediocre whereas Avril had 3 back to back huge albums.

Thankful didn't sell 4.5 million, it's at 3.5 million at best and that's bad for a 2003 album. Breakaway was huge and ever since 2007 she has struggled to sell 2 million worldwide.

The receipts say it sold 4.5 million WW. That's fine for a 2003 album, especially one where she was only just starting to get started WW.

I think it's ridiculous to call her a "one album wonder" or that she "only had one big album", acting like she was only successful for one era. Just because an album isn't Breakaway huge doesn't mean it isn't successful. Most of her albums are definitely considered successful.

It's not fine

I never called her a one album wonder, I just said Breakaway is her only "big" album, which is true.

Anyway Kelly is probably bigger in the U.S, Avril everywhere else.

A one album wonder is someone who is only successful for one album era. Kelly has had success throughout her entire career....just because it isn't massive success like Breakaway doesn't mean it isn't success.

For example, I could definitely argue that Kelly has had bigger and more longevity with singles success in the US (and several other countries) than Avril.

Avril.

How many times does this thread need to be made?

Kelly in English speaking countries (sans Canada), Avril everywhere else.

I'm striking while the iron is hot

Plus the Avril stans are a riot

Avril.

Kelly can still comeback, though. She needs to work on her recording skills (she has the chops, but her inflections are not unique), her music videos and her producers. Her voice is still incredible and she's only ever one great song from smashing.

Avril by far.

Her first 3 albums were huge.

Yes, it is.

Omg does she... Her music videos are so terrible...

But, to answer the question, Kelly. SUBG alone had a bigger impact on the pop music scene than anything Avril's done.