My experience is the best Isobaric setup is a sealed (no port ala Linn Isobaric speaker)), but the box then needs to be bigger to get the lowest frequencies.
Best type of Sub to consider?
For the tightest, punchiest, most detailed lows, it would be expensive but the best would be a "Isobaric" designed sub, it will be large also too get the LF down low.
You’ll to have deep pockets and have to search to see if anyone makes a really good one.
This is how they work: http://www.vueaudio.com/isobaric-subwoofer-design/