There is no better..... but You can certainly prefer one over the other and there are implications of one being better over an extended period of time.
If a ported driver is ported correctly, it will be acoustically flat. If a sealed driver is in the correct encloser and you achieve a final QTS @ .707, you have an acoustically flat sealed driver. The big difference is that it is typically easier to find a driver that will achieve a very low frequency from a ported design and when the driver is at its minimum frequency a ported sub will then roll off @ 24 db per octave, so below its rolloff there is very little output. In a sealed design, once a driver hits its low frequency rolloff, it rolls @ 6db per octave, so you will still have very useable low end frequency below the point where it begins to roll. Because of this, the two do sound a little different from one to the other. Also, I had said that over time the implications are that one is better. That is because as a driver wears, its specs change, especially its qms... as the specs change a ported design has a tougher time maintaining its accuracy, where a sealed woofer will stay fairly true... Of course, that does take a fair amount of wear. As alluded to above by another... Any woofer in its perfect sealed box, will always need a larger encloser for its perfect ported box, But there are very few woofers (very few, not zero) that truly are versitile enough to use ported or sealed. I hope this helps, Tim