Looking to purchase Subs

Hey everyone, I'm new here and my friend had showed me these forums when he was trying to explain to me what subs I should look for when purchasing subs. I'm looking to just purchase subs for my 06 325i E90, originally after hearing my friends system (2 13 W6s + 1000/1 JL AMP) and then only hearing one of his subs, I decided that one of those would be enough. I was recomended to not go with a huge sub and tone down the size to a smaller sub and upgrade to a better performing sub (I guess you would call it that), so I was looking into the 10w7 + 500/1 JL amp, it seemed to fit the bill and I've only heard good things about JL and the W7. The problem is now, that my friend said I should look around at more companies rather then just sticking with JL, because for the same price you could get something better. I don't specialize in subs that much, I have an OK understand of them, but I'd like more info and a path at what I should be looking for in other companies and basically major differences between the subs from one company with the JL 10 W7. So far I've looked at RE Audio and Alpine. I just want to hear people's opinions on what subs they like best.

Thanks,
-Caster