Subwoofers: Ported or sealed?

Sure. Porting a woofer or subwoofer is a way of pushing the speaker down lower flat. The problem is they roll off quickly below that. Sealed subs and woofers are less efficient, start rolling off earlier, but continue on down lower than ported speakers. Ports can make noise. Sealed subs can play just as loud but require more power to do it. Since they go lower you can use DSP and a lot of power to produce very low frequencies. I make subwoofers and will only make sealed ones. I I use 2500 watts per sub with digital signal processing to align the subs with the main speakers. 

Sealed and ported have similar efficiencies in the pass-band. Ported will go down lower.

All my experience and measurements say that the bigger issue is the amount of bass in a room. If you want to plumb the depths of bass with a sub you have to be careful of the placement and use appropriate room treatments and/or EQ as/if needed.

Smaller, sealed subs tend to leave the sleeping dragons alone. They don’t excite the room modes and therefore won’t ruin the sound. It is also true that below the tuning frequency, ported subs climb in distortion due to increasing exertion. They may also be significantly larger than the sealed counter parts.

I use a Hsu sub which has optional plugs. Whether I use them or not has to do with the in-room response.

Having said all of that, if we aren't talking about subs, I built a sealed center channel specifically because I knew I wanted to use it with a subwoofer, and crossing it over at 80 Hz or so would mean I'd get a lot of dynamic range and lower distortion in that configuration than I would otherwise.

Don't forget about passive radiators.