I have to say Reid. He matured visibly through the seasons and now he also looks better than he did in season 1 :)

Well I think Emily changed a lot. In the beginning when she arrived at the BAU, she looked more like a young girl.
And during the last seasons she's grown up, to a 40 years old woman.
I think you could see at her the most that she got older. Well for me she looks now at her best. :D

Great Pick!

Thanks Mak! :D

I'd have to say Reid has changed the most in the past four years. He's not so much of an innocent young boy any longer. His experiences with the girls he's been with, his kidnapping, and his reunion with his father have all shaped him greatly. No one else on the team has experienced quite what he has.

I agree entirely with reidrox.

And this is a great pick by the way (:

-xo.

Thanks tooch! :) I'm glad you like the pick.

This is a though one!
They all changed throughout the years.

But, I have to go with Reid on this one. He changed so much!
Like reidrox and Helga said, he went from a "young innocent boy" to a matured man.
Though, Colette I agree with you too. Emily also changed a lot!

Yes, I know its a hard one. I was also between Emily and Reid.
But I think they made Emily look older through the seasons.

Even though I've only been watching for a little while, as I watched the earlier episodes until the season 4 finale just a few nights ago, there is not only a visible change in Reid, but also an internal one as well.

He went from being an innocent "assistant"-like person to one of the most take-charge characters on the show. Now it's not just about calling him Dr. Reid so people respect him. He commands respect from the people around him because they all know what he's been through, and he's still there.

I love watching him in earlier episodes and being able to see the difference now. I don't think many other characters on television have ever changed as much as Spencer Reid. He's practically in a class by himself, and not just because he's a genius. ;-)

Reid is so much better looking and hwe dresses better now too!His personality has changed imensly also!!I ♥ Reid!!!!!!He rocks!

Prentiss,

Well as Celin79 up there said,
Prentiss was just a new fresh girl to BAU
but now, she;s not

He's grown up. Just look at his drug addiction.

i love him my little spencer is grown up!

Reid has gone from a kid to a man throughout the show.

Physically I would say Reid, but psychologically it is Emily for sure.