As Jeff said, it all depends on you.

In my T-Bird: JVC head unit, stock 6 speakers and two 10" subs wired to a 400 watt amp in the trunk.
In my Bronco: JVC head unit, 4 aftermarket speakers wired to the deck, and one 10" sub in the custom center console wired to a 240 watt amp.

I found both to be a good balance.