i dunno bout the best sound and all that, but from what i understand all the tubing is the same, u could make ur own tubin and it would do the exact same thing. the important part is the filter itself.
but anyways, i just ordered the mazdaspeed one. its made my aem, so its basically the same exact thing, except its engraved with mazdaspeed. it also will not void ur warranty. ive heard mix emotions bout aem voiding the warranty since they do make the mazdaspeed one. but then again ive also heard that its very rare that they will void the warranty due to an air intake, but i think its better safe than sorry.
otherwise ud have to take the intake on and off each time u go to the dealer.
but i dont really think u could go wrong with any of the above, it just depends how much money u wanna spend.
u could also just buy a k and m filter for it if u wanted to do that