In the big picture, what ever makes you happier is the better option.
First, two subs versus one sub is one discussion. Two subs can have advantages in terms of output and being able to get a flatter response across the listening area, but you do have to put some effort into getting them set up properly. If set up wrong, they can cause either big dips in certain frequencies or big gains. There are guides on the main Audioholics site for setting up two subs to help out with all of that, though.
Next, is an SVS or HSU going to be that much better than one or two Daytons? Depends on what model you get and what you want. Do you want shear volume, low frequency response, the best "value," or just enjoyable sound? For many, the answer will be Dayton because of the cost and the bang-for-their-buck. For me, it was an SVS - but not any SVS. I got an SVS PC13-Ultra because I wanted to go below 20Hz, and the company had a great rep back in 2007 when I was shopping (and I've been very happy with them since). Doesn't mean that I get much audio response below 20 Hz from the sources that I play - but I wanted it, and I knew that I wouldn't be happy until I had it...so it was the better choice
for me. An SVS NSD model wasn't going to give me what I wanted, so even within a brand, there are models that may not fit what you want.