Tough choice, I would say 2003:

Rappers like Ludacris were getting #1 hits in both 2003 and 2006. Beyonce's B-Day album sounds closer to her debut than Sasha Fierce. Lady Gaga and  Katy Perry were unheard of in 2006. Pop punk and post-grunge were still going strong like it was in 2003 while in 2009, they were decreasing rapidly.

It's closer to 2003 of course. Like you said BDay sounds closer to DIL. Kelly Clarkson was still releasing pop rock songs, as opposed to the electropop sound heard on her 2009 album. Rap was more popular in 2006 compared to 2009. 2006 is when southern hip-hop completely took over. In 2003, southern rap on the move to becoming the most popular subgenre of rap. In 2009,  you still had southern rap but it wasn't as popular. 2003 and 2006 was when urban music was extremely popular. In 2009, more pop oriented music started to take over.

In 2006, you still had songs like these playing that sound early 2000s

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I went with 2009. 2003 as an entire year outside of music just felt too different from 2006. In terms of music tho I would say 2003 is very unique as well as 2009. In 2003 you had reggae fusion which was not much of a thing in 2006 (minus Sean Paul’s temperature/ give it up to me). In 2006 you had new artists like Chris Brown, T-Pain, Keyshia cole and Rihanna which made similar styles of music up until 2008-2009. R&B from 2006-2009 pretty much sounded the same and really began to plummet and go into a different direction in these years compared to 2003 where R&B was still the dominant source of music on the pop charts. R&b still had a late 90’s influence to it in 2003 and sounds too early 2000’s to even be related to 2006, where as r&b in 2006-2009 was mostly influenced by synth pop.

Hard to say. In terms of hip hop, 2006 was the transition from the Silver/Jiggy Bling Age (50 Cent, The Game, DMX, Eminem, Missy Elliot, Prime Jay-Z, Nelly, Prime TI, Early Kanye, Ludacris) into the Bronze/Ringtone Swag Age (Rick Ross, Jibbs, Yung Joc, T-Pain, Soulja Boy, Out-of-Retirement Jay-Z, Gucci Mane, TIP-era TI, Timbaland, Prime Kanye, MIA).

It was like neither since it was in the 2005-2008 era, but if I had to choose I'd go with 2003.

Closer to 2006

All right, well in 2006, you had emo rock, crunk, pop punk, post-grunge, snap/ringtone rap and contemporary R&B being popular genres, so it's neither like 2003 or 2009 for the most part. But 2009 had the electropop invasion, and 2003 still had contemporary R&B being the most popular genre at the time. So I guess it's closer to 2003, but not by that much.

Bump

I say 2003, because you still had pop punk kinda still around, with All American Rejects and nu-metal like Linkin Park still being pretty huge

Bump
2003

With B2K and P Diddy's "Bump, Bump, Bump"