A single 1723 Subwoofer 1V vs a single 1723 Subwoofer 2V is an easy answer, the bigger one is better. It has dual drivers in a push-push configuration that cancel out any side-way force and it couples better to the room as well. Obviously, it has more headroom and output with dual drivers and a 400W more powerful amplifier.
Dual 1723 Subwoofer 1V vs a single 1723 Subwoofer 2V on the other hand is a much more interesting question, and there is no straight answer to which solution is better. It depends on some factors that we will look closer at here.
With achieving the smoothest possible frequency point in mind, a setup with dual subwoofers is hard to beat as you can move them around to get the best integration possible in your room. While this will give the smoothest response for all listening positions, it may affect maximum SPL compared to either stacking them on top of each other in a corner or using a single larger subwoofer.
Placement in a corner will help the subwoofer have a lot more output in the deep bass compared to having it in the middle of the wall. One of the negatives using dual 1723 Subwoofer 1V with them placed with a distance apart is that they will not acoustically couple on the entire frequency range meaning you may only get +3dB added output from adding a second subwoofer above a certain frequency point, instead of +6dB output that would be achieved by stacking them on top of each other. In that sense you get more output for the money going with the larger 1723 Subwoofer 2V.
It really boils down to maximum SPL vs best frequency response in your room. If you are hunting for SPL then a single 1723 Subwoofer 2V will be the best option, and on the other hand dual 1V will be easier to get a smoother frequency response in your room.