It's not always a good business decision to buy a piece of equipment because it's "the best."
I know some studios that literally went under when they purchased drum scanners (and yes, printers) because they were "the best" at the time. Unfortunately, they were soon outperformed by much less expensive equipment, leaving those who had purchased "the best" to try to compete while still making rather large payments on outdated equipment.
Also, the z3100 hasn't been in use long enough to truly evaluate it.
That said, I may purchase a z3100, but the price of the ipf5000 is just a little too attractive right now, and it would probably suit my needs.
Giving it a little time to see if HP is going to offer any reductions, rebates or other incentives on the z3100. If they don't, my choice is easy: I'll go with the Canon ipf5000. Also hoping the ipf6000 will come in at a better price than the z3100.