The speakers do crackle, but only on games with really loud sound effects and music like Mario Kart 7. They're also a lot quieter than the regular 3DS at full volume. I always play with headphones though so it really doesn't matter, at least for me. In terms of portability, it is harder to carry around. I always carry a bag though so again, not an issue for me, but I have put it into my pocket before and it fits but almost half of it sticks out. Unless you have really baggy pants with big pockets, it will be sort of an issue.
I have the blue mario kart bundle and I love it. I was torn between it and the cosmo black but I really enjoy the bigger screen and I have no regrets.