Red Bull boss Christian Horner expects the Lotus and Sauber to be strong in 2013.
"All the others are still difficult to assess," added Horner.
The German magazine's correspondent Michael Schmidt said the new grey Sauber had Nico Hulkenberg "smiling" all week as the opening test at Jerez unfolded.
"Eyewitnesses say the C32 is the best car in the field in fast corners," said Schmidt.
Swiss newspaper Blick's veteran correspondent Roger Benoit, meanwhile, quoted Hulkenberg as confiding to his Sauber colleagues: "Guys, this car goes like the devil."
As for Lotus, both Romain Grosjean and Kimi Raikkonen each tasted the top of the timesheets during the four-day test.
"We are quite surprised," admitted the always-grinning Frenchman Grosjean, according to RMC. "I think everybody saw my smile."