Well the alpine are louder at 300w but the frequency response is from 65 hz where as the jl are 100watts but they lave a lower 59 hz frequency response.
Both have statements like gives thunderous bass etc.
If your going to spend your cash then i would suggest you get your favorite cd or mp3 and go into your local store and price them up they may be just as cheap in a store than online.
But in a car stereo store you will be able to hear them, and this is very important because your ears may prefer either one, so it's best to try and hear them perform before you part with your cash.
I'm pretty sure they will both sound great but only you can truly know what sounds good, unless theres been a test of them in some car stereo mag like ''car audio & electronics'' mag you have there in the states..
On searching for it i think they have gone bust, thats a shame because they used to review all the alarms n stuff..