It turns out, according to Optoma, that the H31 (already on the market for 9 months as of this writing) has been so successful, that they are continuing to sell it, while bringing in the H27 as well. The H27 offers a number of enhnacements over the H31, and a slightly lower price. Truth is, however, few home theater projectors sell briskly before the word gets out - in the form of reviews, so Optoma's strategy makes sense for the next couple of months. Offering the same brightness as the H31 projector, the H27's performance should ensure its position as not only a truly improved replacement for the H31, but as a strong contender as best home theater projector. Since you are going to ask, overall, I would recommend the H27 over the H31.
The Optoma H27 projector is a widescreen projector, with WVGA resolution. It claims 850 lumens and has two different contrast modes. The standard contrast is 2500:1, however for best performance there is a 4000:1 contrast ratio. This extremely high contrast ratio is the result of Optoma's "AI" circuitry. Like a few other (top rated) projectors (Panasonic PT-AE700u, BenQ PE7700) the H27 projector is using frame by frame image adjustment to enhance picture quality, and Optoma H27 projector owners are benefiting from the results. The H27 uses the 854x480 Darkchip2 DLP processor, which is the heart of this projector's performance.