Jimmdavis has good advice, experimenting is key. I've done it both ways. It often really depends on where you set the crossover, the sub's capabilities, and on your room/placement.
The only way to really get proper bass response is to install bass trapping, if you have not done this. I use Realtraps and they are spectacular. Easily one of the best purchases I have ever made. Then all your equipment will sound better, and you may decide that you do not want *any* subwoofers. But at least can make a true decision about the quality of bass.
If I have to go to 70-80 Hz with the sub then I would usually prefer two. For most of my recent setups I only need <35 Hz, so that works better and simpler for me with one sub. And when I do it that way I prefer the overall sound with the single in my rooms.
Also, the sub's performance will matter. Even if the filter is low, if the sub is producing a lot of harmonics then you will be able to localize it, and two can help minimize that effect. Better subs tend to produce less of these extra frequencies.
For music, if you have good mains and room then it really doesn't take much contribution from a subwoofer to balance out the last octave.
Steve