I found the 5d's jpegs pretty good at low ISO really nothing to see details wise v Raw. At high ISO not bad either but the KM5D was generous with exposures which helped too. DR yes a bit more in raw as expect didn't really have a problem or concern using jpegs most times.
Pentax were when I was using them doing a good job on jpegs that seems to have changed in recent years. Nikon were always consistent NR off was quite low managed to keep decent details and get rid of most colour noise. Fuji another maker who used to be good X10 happy with them, XE1 was also very good. More recent models suffer from the blow torch v candle wax issue I have no idea why they changed them if it ain't broke
Can't comment on Panny or Oly though Oly tonality is nice as is Fuji. Canon I have less experience with the jpegs I have shot was pretty happy with them.
Sony never warmed to the jpegs at least the older models wasn't that happy with them NR was odd not really removing enough colour noise too much detail loss and the low/off settings not really low enough. Newer ones can't say (A77II, A68, A99II etc) maybe they are better seem to have improved a bit. Rarely use the jpegs on the Sony's I have at the moment. Not everyone like the KM5D colours I did great for skin tones it did push the reds a bit more than some makers and you could clip the channel if you have a bright subject (dial back a bit). Canon also liked a lot with people I know I find them quite nice tonality wise. Colour balance is such a big factor too Nikon tended to be cooler (sometimes D7K was) sometimes a bit yellow (D90 was a bit like that)