I had a Sunfire, and it doesn't belong in the same group and MJ Acoustics and REL. The Sunfire is of the compact home theater genre of dinasaur stomping room shaking subwoofers, whereas the MJ Acousics and REL are of the few subwoofers truely disigned to augment music well.
If your preference is music and you want your speakers sound natural and 'larger' than they are, then REL and MJ Acoustics are the way to go. However, the MJ is made in England instead of China and has a remote with four programs which is very nice, along with a better price. For a musical sub, to me the MJ Acoustics is the clear winner. I have found those other, super deep room shaking subs to sound uncomfortable for extended listening and out of place with music.
If you love good music and extension and that is your primary reason for wanting a sub (and sicken a little in your stomach at excessive unsettling ultra deep bass that doesn't blend well), end your search for the ultimate musical sub and buy an MJ Acoustics.