If you are interested in accuracy, go duals, because they can do a lot more to smooth out frequency response than any single sub can. There isn't a bad choice on your list, although I don't know how the Rel compares to those other subs. If duels need to be compact and fit in your $1500 budget, I would go with the SB-2000s. If you can stretch that budget a tad and consider them compact,
dual Hsu ULS-15 mk2s would give you pretty unbelievable levels of output and overall performance. I know all the other subs are good, but duals of any of the others would blow your budget past $2k, except for the Rel sub, which I would shy away from since there is no available performance data for it whatsoever.