JPEG, with Contrast, Saturation, Sharpness and Noise reduction all turned down to the minimum. And AWB adjusted towards Amber on the Amber-Blue axis and towards Magenta on the Magenta/Green axis.
Because of the way I work, my subject matter and the type of pictures I like to produce, some of my images can be problematic out of the camera (e.g. noisy, underexposed, desaturated, needing shadows brought up or highlights brought down, needing things cloned out or non-subject areas stretched or squashed). By and large I have not found JPEG unduly limiting in what I can do to them, although I expect some extra headroom for highlight recovery would occasionally be useful.
I am trying some RAW + JPEG sessions with comparison processing of RAW and JPEG versions of the same image. I know that because of the increased bit-depth of the RAW images, and the lack of JPEG conversion, that the RAW versions must contain more information. However in my (very limited) experience to date I have not been able to exploit this to produce better-looking results.
This might change of course with more experience of RAW processing, but I'm not sure I'm going to get that experience. The reason is that I shoot mainly close-ups in the field and I need the camera to stay responsive, including when I take a lot of shots quite quickly. Odd as it may seem, the same applies to my other main subject matter, sunsets, where many of the images are panoramas and I also need to work quickly and continuously.
With RAW the camera becomes unresponsive and the shooting experience is punctuated with delays that break the flow of my shooting, reviewing and concentration, and I sometimes lose control for opportunity-losing periods.
There are some other issues that I could mitigate by spending more on PC equipment, although I would rather not. Uploading to the PC the 1,000 - 1,500 images that I capture in a busy day does take a long time. And RAW + JPEG takes a lot more storage than JPEG. Also, I'm finding Lightroom (and Silkypix) frustratingly unresponsive and slow compared to Freestone and Photoshop, both for reviewing/comparing/selecting images and for processing the selected images.