For what it's worth, I like the Akrapovic carbon fiber.
I don't have one but while is hard to get a really Accurate feel for a pipe on YouTube, it sounded the nicest to me. With the baffle in it didn't sound loud enough to piss off the neighbors and had a nice deep tone.
Without the baffle it seemed god awful loud.
Hindle would be my second choice.
The Leo Vince Evolution II would be my third choice.
The Two Brothers and Yoshi are too loud for my tastes.
There are more makes out there.
Do a 2011-2012 CBR250R exhaust search on YouTube and you'll find many vids of different pipes.