that's like asking I want a sports car. are you going to road race it? daily it? track it?
If you wanted a flat response Id say go 5 tuned to 28 if you want a street beater 2.25 to 2.5 tuned to peak around your cabins FS of tuned around the lowest frequency the music you listen to will play down to. I never recommend tuning about 40 unless you want to compete. generally those woofers are low-end monsters so a lot of guys do 2.5 tuned to 28-32hz
3 cubes after displacement with port 3.5"x10" tuned to 28hz. //content.invisioncic.com/y282845/emoticons/yumyum.gif.0556df42231b304b9c995aefd13928a8.gif