best sub for overall performance

im not looking for something that is cheapo im looking for a very nice sub that has good responce and a good mix of sq and spl more spl than sq but it is alwasys nice to have some sq. im looking at a sub for my room and have decided to go with a titanic 15'' mkIII it has good responce and is able to hit deep you could also put it in a car if you hafve the space. the specs say that it is a one way xmax and i dont no what that means i gess that it means that it only fires one way.

Aaron