This a hard one for coaches, I reckon. You want to squeeze your best players into the starting XV wherever possible (see Horwill playing at 6 in the opening game last year so Byrnes and Van could also start).
However how often do we say that it is the quality sides who have depth in the bench. In terms of impact, I think Simmons has the ability to up the tempo as a fresh man late in the game, however Van wouldn't be able to provide the same impact. I can't recall how often Dave Giffin ever came of the bench because he wouldn't be able to have that energy. I reckon Van's in the same mould.
Unless they really separate themselves from each others in the trials, I'd imagine Horwill and Humphries will start with Simmons on the bench... particularly for that second round against NSW.