she was talking about Gaga

From this list only Katy Perry's latest lead single is a good song and it's only a little bit better than I Kissed A Girl.
Beyonce's RTW has amazing vocals of the queen though. Diamonds and Applause are annoying because they don't even have nice vocals.

Lady Gaga

Rihanna. IDG why people are voting Gaga when she just churns out the same generic dance tracks

Rihanna obviously, every album sounds completely different and is a different genre.

Rihanna has changed a lot but she takes baby steps each year. I voted Gaga.

Rihanna. Her debut single was not very good, and "Diamonds" is a pretty good song.

Katy, Lady Gaga and Beyoncé all started with great songs, and Lady Gaga and Beyoncé have regressed when comparing their debut singles to their latest lead singles. Katy would've gotten my vote if her debut single wasn't so much better than "Pon De Replay."

Rihanna

Definitely Rihanna

Gaga and Beyonce started strong and keep going strong. Katy is like a tween pop artist. Theres no growth, nor is there need for any.

Rihanna

Some of you are as shallow as a fisbowl. Quasi dabbling in multiple genres isn't an indicator of "growth" in and of itself. If anything it's a more a sign of disingenuousness. And that some if you are actually using lead singles as some kind of measuring stick for growth further proves that you should be somewhere playing with big blocks.

Artistic growth is becoming stronger and more capable in the way you personally present your craft, it's also showing more maturity in your overall image.

This eliminates Rihanna entirely.

After 7 albums she's still a mediocre singer, piss poor live performer and her overall attitude tends to be unprofessional, juvenile and basically rotten. She's actually grown the least and has probably regresed.

I was just about to express this same sentiment. I couldn't have said it better.

Rihanna.

Rihanna