I believe the ideal is to have a center speaker too, and I have one, but I have heard systems improve when run in phantom.
It's too hard to say it's better or worse, straight up. The first response here already nailed it: You gotta try and see for yourself.
The reason why I think certain setups work better without a center speaker is because their center speaker really sucked, at least when functioning in a horizontal manner. Then sometimes it is placed on a resonant cabinet, perhaps shoved in between shelving, and the whole hodgepodge of reflections, resonances, diffractions, and lobing could be avoided with phantom. It just depends on the setup in the end I think.