While it is important to have a good quality amp, the box makes the speaker.
A buddy of mine had a kicker cvr 15 with a good amp running plenty of wattage stuffed into a generic sealed enclosure in a little honda, he had it metered at 132dB. I purchased a kicker cvr 10 and built a proper enclosure to use in my explorer, and ran it off a crunch 800w amp (crunch amps are built with hifonics components for those who didn't know) at any rate my 10" sub metered at 131.7dB playing the same exact song as my buddy with the 15" I later upgraded to a cvr 15 in a proper enclosure and metered at 146dB on a larger amp.
my advice for the OP is don't go for most of the brand name stuff they sell at best buy. JL, Alpine, and Kicker I've had good results with personally, but they are all overpriced IMO. I've had good luck with MA audio, Audiopipe (only their higher end stuff), Hifonics, or if you want to get into the expensive stuff there's always MMATS, Digital Designs, Memphis audio, RE Audio, Fi, etc. Regardless of what brand you buy, stay away from entry level speakers, most of the entry level stuff is junk. If you'd like further advice, feel free to pm me.