Paying the shop a visit to play with the cameras will usually allows you to make a better decision than what anyone can say. That said, a week ago I was deciding between the LX3, DP1 and the GRD2, and in the end I got the grd. I recommend visiting MS Color.
Chances are, if you are looking for manual control, none of the 3 cameras will disappoint. Though if you use autofocus, DP1 may be sluggish in that aspect.
In terms of sensor quality, the DP1's sensor is larger, so it's bulkier. Thus it can only hold up to a F/4 lens while keeping the form factor small. It's lens is very sharp wide open though. The quirks with the camera is a lmit of ISO setting at 800. It's a no brainer: F4, ISO 800, no image stablization means it's a poorer handheld camera in dim lights. But the sensor quality makes up for that drawback I think.
The LX3 iq is probably one of the best one to date for a small sensor compact. It handle noise very well at ISO 800 and is the camera to use if you want to shoot raw(which for this one you should). F2.0-2.8 lens and OIS makes this a good performer in low light handheld.
But at the end, I went for the grd2. I think this camera has character. It felt the most robust in my hand, and is truely a compact. I can change settings very quickly, and have a mode dial to store two of my custom setting. ISO 80 jpegs are fabulous. It can get very noisy at ISO 800-1600, but imo there are good and bad noise. The ones on the grd are what I consider good noise often creating pleasent grainy effects which I like.
Note that if you are going to shoot with high ISO though, you will want to shoot raw and it's not exactly the fastest camera for that. You still need a fast SDHC card for best performence.