It seem like the only sub I'm recommending these days is the SVSound PB12-NSD

I'm recommending that sub all over the place!
But there is a good reason for that - it is simply the best performer at its price point and a lot of people are looking to keep the budget relatively low, so the PB12-NSD gets the nod from me every time!
I have nothing against the other subs that were mentioned. But they are all just a little more expensive than the PB12-NSD and, especially for Canadians (like myself), much more of a hassle to obtain.
I actually have dual Epik Sentinel subs on the way to me as we speak! But my choice was very limited due to some strict size requirements. For getting the Epik Sentinels into Canada, I had to pay Epik with a Money Order (not something I would normally do, but I trusted Epik enough and all went well

) and I had to have them ship it to a package forwarding company and pay a hefty additional shipping charge to get them across the border. If you know someone close to the border and you can go pick up the sub yourself, that would be a much less expensive way to do things!
Anywho, HSU and eD will ship to Canada for fairly reasonable rates. But in terms of performance gained for dollars spent, you really cannot do better than the PB12-NSD and getting it from Sonic Boom Audio here in Canada.