It is impossible to say for sure which one has better contrast unless someone objectively measures it VERY VERY carefully and A/B's to ensure what they measured matches what their eyes saw. I would bet that the Mits hc4000 has better on/off than the Benq by a bit, you also cannot trust on/off measurements though. Sometimes if it is measured by the same person, you can trust them a little (sometimes, not always).
Another indicator of contrast (although not scientific, it's just a TREND indicator), is that how many lumens at WHAT wattage each projector produces in ECO modes (although this matters more if comparing two models in the same brand). However, if the wattage of the two projectors are the same, and they both have DC3, it is probably unlikely a significantly brighter DLP projector at the same price-point is producing higher on/off or ANSI contrast (being the Benq, so Mits should probably win). This is because they can't get the light pollution out of the DLP mirrors and there is some direct relationship to how much light there is, and they have to add more expensive components to make it handle light pollution in the mirrors and lens (and they can't with PJ's at this price).
The Benq has DC 3 and so does the Mits, the Benq is a much brighter projector indicating they opened up the light path more (but it is probably higher wattage too, so maybe not that much more).
That said, so far there hasn't been a projector that can measure as high in On/Off as the Mits for its' price, and Benq doesn't have a great history of high on/off or ansi contrast in their lower-priced projectors, so if I were a betting man, bets are on the Mits.
Still with 2D only for the Mits, I'd buy the Benq instead.
Edited by coderguy - 1/1/13 at 7:17pm