depends on how much you're looking to spend and what kind of quality/longevity you're looking for..
i love my all alpine setup, but it cost me a few bucks to put together. has lasted me for quite a while though, and i see them staying for quite a while longer
on the other hand, i've installed plenty of cheap-ass dual garbage that actually pounded pretty good. they don't last as long, but they get the job done cheaply.