No pour is better than a floating pour for signal integrity reasons. When you have a floating pour you are increasing the coupling capacitance between signals so you are increasing the chance of cross talk. In general the pour that is grounded will perform the best, but you should be aware of image current flow.

If you're etching it yourself, you should add copper pour connected to nothing. If you're having it etched by a PCB fab, then leave the board without a pour.