I'm getting ready to purchase subs for my truck, but I don't know which is the best.  Could anyone help me decide?   I was looking at subs from JBL(p1224) , MTX (8500), Alpine (type X), and Morel (Ultimo).  I'm looking at getting either in 12in.  

check out the icon series, very high end subwoofer.  1000wRMS.  http://www.soundsolutionsaudio.com/products/icon/12.html  

http://www.soundsolutionsaudio.com/products/icon/12.html

sorry here's a clickable link    

Hi there, there's lots and lots of brands to consider even more to stay away from.  Your list there is a good one and the Icon recommendation is another good one.  I'd also recommend the Phoenix Gold RSdC12 which is the newest version of the old RSd12 which has gotten rave reviews.  A smaller company called Audioque has some incredible subs and amps at prices that are heart attack worthy for the performance they offer.  Incriminator Audio is another less mainstream brand that makes out of this world subs.  RE Audio has a lineup that should make you drool as well.  These are all brands you can EASILY trust putting your money into.  Just make sure your installation is matches the quality of equipment you're purchasing.  I have personally seen low quality subs outperform high quality ones because the nitwit who blew all his money on high end subs put them in a cheapo walmart type prefab box that it wasn't designed for while the low quality sub was in custom boxes that matched the subs specifications.  Good luck and have fun!