Compare to what? If you're talking each other, then unit to unit the Vex are better but Oryx and his siblings are so incredibly powerful that the Vex have already accepted the fact that unless something completely unforeseeable happens (like guardians killing Oryx) that the Vex will inevitably be consumed by Oryx. If you're asking how the Hive and Vex compare to the Forerunners or Precursors, that's not even fair. The Forerunners alone are many times more powerful and advanced than either the Hive or Vex and the Precursors are basically gods, able to control the very laws and fabric of reality and life at will.

I meant how do they compare to the Forerunners and Flood.

We'll both can and would be infected by the flood. Also they're technologically and numerically inferior to the Forerunners. The Precursors are so incredibly powerful they could probably solo the entirety of Destiny's universe.

The Vex don't have a neural network, so they couldn't by infect, they are still susceptible to the logic plague and the Flood can still consume their bio matter. Oryx and his siblings have personal universe that they can control. So it would be a stalemate as both sides can warp reality.

The reality warping Oryx can do isn't the same as what the Precursors do. Oryx is able to manipulate that which already exists is some limited way by Taking, but cannot himself call something into existence. The Precursors can. Also between the Shield worlds, fortress worlds, and other such super weapons while the Forerunners may not be able to kill Oryx in his Throne (I think they could given their power and ambition but we'll assume they can't) they could still kill him physically with ease and reduce him to a non-threat by just killing him every time he reclaims mortal form and, for lack of a better word, spawn camp him with a small fleet for eternity.