Mercedes have had 3 DNFs this season, Renault have had 2. Mercedes have had a double DNF at Austrailia and one DNF at Monaco with Schumacher.
Both of Renaults DNFs have been down to accedents, and the last 2 races have seen them with Petrov at Monaco and Heidfeld at Canada.
Not that the Renault guys cant look after their equiptment, it says that the Mercedes guys have slightly less relyable cars too.
However, lets look at non classified finishes now that have finished in non points paying posistions;
Mercedes: 4 = 2x P12 (ROS - MAL/MSC - TUR) 2x P11 (ROS ESP & CAN)
Renault: 3 = 2x P12 (HEI - AUS/CHI) 1x P17 (PET - MAL)
So it looks like that the Renault is a faster car so far.
Now ill have a look at points paying posistions that dont finish on the podium;
Lets have a look at Poidums now;
Average posistion finish, to my data says that the Renault is 3.37 and the Mercedes is 4.00. Quali pace is better for Mercedes with an average place of 0.707 so far, Renault is 1.024 so far.
The mercedes is the faster car, however its just not fast enough in the race. I also think that Schumacher and Rosberg can get more from the car, just the car is holding them back a little, to the point that Renault has is more relyable and quicker to the finish line. Also Petrov is better this year than last, and Heidfeld is the safe hands that Renault wanted to get to replace Kubica, who on analysis could have mullered the car into places it should have not been in.