All other things being equal, an open web truss will allow more deflection than a closed web alternative of the same dimensions. The difference, however, is that the designer should take this into account in the design. That is, if the span requires a certain size closed web truss, it will likely require a different size open web truss. You can't just interchange the two like for like. This also limits you with floor designs on upper levels. If you have a weight bearing wall that must be supported mid-span of your floor, then it becomes more difficult to use open web trusses because they are not as "strong." You get to a point where you are size limited. That is, you can probably design an open web truss for any application, but if it needs to be 36", you probably will not be willing to give up that much headroom in your basement. Again, it all comes back to the floor designer understanding the constraints of the problem.
With regard to engineered floors vs traditional (I'm assuming you mean traditional dimensional lumber) then engineered floors will generally result it an a much flatter floor as well as reduced deflection. Our framers said they rarely use traditional floors anymore as they couldn't prevent squeaks with traditional lumber.
EDIT: I should point out that my experience with these products is limited, but I did quite a bit of research when discussing the flooring with my builder. This is the way I understand it, but it's subject to being completely incorrect