I think the B&W is better than the REL, but although I haven't heard the MJ I would give it a try as I think it could be better than both the above... I swapped my ASW600 for the ASW675 which was a huge improvement...
The ASW675 would be very nice, but its very much more than I can afford and something else would have to give to pay for it. Hopefully the ASW600 (or the others mentioned) will more than do the job...
Go take a listen to the subs mentioned above. I'm not sure I agree with the assertion that REL's reputation is falling.. their subs are first class and up there with the best. I have a Strata III and a Quake, so I guess i'm biased, but I went and listened and liked them the best (for the money). I suggest you let your ears decide.