I prefer the Merrill cameras because they have a true Foveon sensor with the same number of pixels for red, green, and blue. In contrast, the Quattro cameras have only about a third as many pixels for green and red as it does for blue. So the Quattro images don't look as sharp to me - although the performance is better with the Quattro sensor.
I have the DP Merrill cameras and the SD1m.
If you are willing to take your time and are in bright light (unless shooting B&W), the image quality is amazing. But you can't go above 400 ISO (unless interested in B&W). Battery life is VERY short for the DP Merrill cameras and the performance is VERY slow. It takes several seconds to record a single image to a card.
You have live view on the DP cameras but not on the SD1m.
The DP Merrill cameras hold their price pretty well which is amazing for a compact digital camera. That shows that high regard people have for them.
I suggest that you start with the DP2 Merrill and give it a try. But be careful - you can get hooked fast and you may find yourself wanting more focal lengths and get an SD1m.
I thought I was having battery problems with my SD1m but it turned out to be bad third party batteries. So now I am back using the SD1m after over a year on the shelf.
I don't think I will buy the upcoming Sigma Quattro SD - I just don't care for the Quattro sensor.