My personal opinion is that both have their pro's and their con's. The LSX is generally faster stock for stock(minus the 03 cobra). I was going to say a whole bunch of shit, but it boils down like this, the LSX powered cars are superior IMHO to the mustang(again, minus the 03 cobra). THe cobra is a well built car. Responds to mods well. Only flaw is the high speed engine lock ups. Therefore, don't drive like a maniac or a ricer and you in the money.
.02
Jackson