There isn't a single best subwoofer, regardless of money you can throw out for it. The only thing we can do is lead you in the direction of subwoofers that will accomplish the purpose you're after, both reliably and within your price range (which you have none, so that helps). You don't want "good voice" from a 12" subwoofer. A subwoofer is designed solely for low frequencies, and shouldn't run over 100hz usually. Vocals and treble should come from component speakers in the front of the vehicle, and since price isn't an option, price of component speakers will also be of no issue to you. Subs that hit hardest and those with great sound quality generally oppose each other when you're talking about the extremes of either, however there are subs that will generate plenty of SPL and sound great doing it, but most aren't going to be SPL trophy winners, they are designed to be a "jack of all trades" so to speak. That being said, the JL Audio W7, the Image Dynamics ID Max, Resonant Engineering X.X.X., Adire Audio Brahma, Eclipse Titanium, Treo subs, and many others are more than capable of delivering SPL and SQ, and doing it well. All are able to destroy your hearing and put out SPLs past the human threshold of pain. I doubt too many would come out of your car saying it isn't loud enough, unless you destroyed their hearing in the process, but after that point a whisper wouldn't be loud enough for them.
i tend to disagree with the xplods being the best. it all depends on the sound quality or what ur ears tell u is the best. different people have different tastes. a component i would recommend is the mb quart m series components. great crisp quality. a thing that suprised me is how the cone is built. it hardly moves while making the greates, loudest sound. i dont hink their is the greatest component either. it just depends what ur ears prefer. i got 2 6 1/2 component pair and a pair of 6*9's for 440 total. i think i couldve gotten others for less bucks but my ears went for the mb quarts