My experience is with Canon, Nikon, Leica and Sony cameras. I mention this off the bat because I don't think all processors work equally well with all cameras and I think that part of what separates the image quality from one processor to another is the profile qualities.
My experience is they all are capable of great image quality, but I can get there faster with C1 Pro. With C1 Pro, you can easily review, edit and process images and export them to multiple file types. I'm not sure what it is about C1, but images seem to have more color depth and more life to them.
I think you can do the most image tweaking with RD, but there is a big learning curve and it's not fast. A lot of what you might do in Photoshop you can do in RD and at the raw stage, but you are not going to fly through processing a huge shoot with it.
Lightroom is probably the fastest since you are archiving and there is no need to process all your images, only the ones you need to print, archive or send to a client. I would think Aperture fits in here as well. Lightroom is also exceptional for upressing an image. In my experience nothing can touch it, though I have never tried huge enlargements with C1.
You might throw Raw Photo Processor into the mix as well. I think it is capable of good results, but I'm not sold (though I did actually buy it). RPP is very limited, but if the image has to go into Photoshop anyway, who cares? There are some things it still does way better than any raw processor.
Ultimately a raw processor is like any piece of photo equipment -- some are better than others, but in general you will get the best results from the one you know the best and use the most and doesn't get in the way of your vision. I think you can make an acceptable workflow from almost anything.