Jenson Button has said that Mercedes have shown a consistently quick pace during pre-season testing.
The Silver Arrows have signed Button's former McLaren teammate Lewis Hamilton for the 2013 Formula 1 season, which gets underway in Australia later this month.
The 2009 world champions told BBC Sport: "I really don't know who's quick. But the one team that has been consistently quick has been Mercedes more than anyone else.
"I like driving [the 2013 McLaren]. It is a nice car to drive. There is nothing that scares me with it but I still feel we can do a lot more with it than we are at the moment, and that's the exciting part, that we're not at the end."
Button finished the second day of the final winter test in Barcelona with the second-fastest lap time, while the Mercedes was 10th.
