SQ is preference, some people prefer sealed over ported and vice versa. sealed is usually flatter on paper. tuning to 25-28hz in a ported box will usually sound smooth with the right driver. some people prefer the sound of a dc level 5 over a lms ultra. some people think prefab kickers sound awesome.
you have to find what you like, what kind of response and volume you want to attain. if you want flat response, go sealed, and then get a driver that's based on sq such as a TC sub, a SSA xcon or icon, maybe fi q or ascendant havoc at that power handing. if you want a powerful low end and no boomy response do a smaller ported box tuned low.
my ultimate sound quality system i ever had was 3 tc-3000 15's in 15 cubes tuned to 22hz. yes it was 155db plus, but i absolutely loved how it sounded. some people hated it. find what works for you