I can personally vouch for the PB1-ISD. It integrates seamlessly (to use a cliche) with my M22ti mains. The only drawback to the PB1 is its size. It takes up a rather large chunk of space. If you take size into consideration when figuring out your best bang for the buck, I think the VTF-2 wins hands down.
The 25-31 is also great. I performs similarly to the PB1-ISD, but you can tune it by plugging one or two ports. Also, the cylinder design takes up much less floor space and is easier to tuck into corners.
You basically can't go wrong with any of the three subs you're considering.
