I should have mentioned, I got a vented box for a single 12, passenger side. Haven't got past pulling it out of the shipping box and giving it a quick look but my first impression is very good. For the price, the quality appears great and the use of the plastic bowl is really clever. I've built a few custom fiberglass boxes and they turned out good, but I'd much rather buy something pre made and avoid the week long process of a homemade box. It's gonna be 3-4 weeks before my install is done, I'll update this when done.
As for the original topic, I like vented over sealed, but only if it's done correctly. Low tuning (30-35hz) is the key, and making sure the sub is matched to the box volume. The output and efficiency is just better if it's all working right. Look at almost any premade speakers you buy, even most computer monitor speakers are vented. You get more output and sound quality *can* be every bit as good.
But if it's not possible to get everything just right vented, just seal it and it'll be better. Sealed is much more forgiving, it saves a lot of fabrication work and space. They both have their place for sure.