Sealed or not is irrelevant. Room acoustics are. Get a sub with an equalizer, then you can match it to you room.
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Actually, sealed or ported is not irrelevant at all. Given the same size cabinet a ported box will allow lower cleaner louder bass; sealed will have better group delay and might be better suited for typical music.
I agree that having EQ somewhere in the system is a definite advantage, though having it only on the sub channel has limitations.
Unless your room is quite small, I would not consider anything less than a 12" driver.