If that CV subwoofer uses an 18" driver and has a bass response down to 35 Hz, then it's very clearly aimed at pro audio markets where maximum output matters more than maximum bass extension. The Hsu and SVS subs are actually rated to go deeper than 35 Hz, but they also likely won't play as loud (won't matter much in a small to medium sized room). As Kex pointed out, you will get progressively more boundary reinforcement as the room gets smaller.

Generally, the choice in subwoofer depends on the room, and what the listener wants. A 10" subwoofer can go deeper and louder than a 15" sub. But, it would also require a more powerful amp, and you potentially have more distortion. There are no hard and fast rules about which one is better.

Hsu and SVS are very credible choices, so you won't really go wrong with them. But, the key to getting quality bass comes down to proper placement, calibration, and acoustical tweaking. On the latter point, you might want to do a topic search for the Behringer Feedback Destroyer and room acoustics. The BFD is used by a lot of home theater enthusiasts to equalize their subwoofers, and IMO it makes every bit as big a difference as the choice in subwoofer. You'd be amazed at how much better a sub sounds after getting EQ'd and properly calibrated.

We've had plenty of discussions on that topic, so you should look them up.