Sebastien Buemi, Red Bull's reserve driver in 2012, spent time watching Wednesday's Barcelona test action from a trackside vantage point.
"I like the Red Bull and the Force India the best," said the Swiss, after Nico Hulkenberg set the surprise pace.
"(McLaren's Lewis) Hamilton and Hulkenberg can brake late and get back on the gas early.
"You can tell that the Red Bull has fuel on board, but still the (RB8) is very good. But you can see that the tyres are old," explained Buemi.
He was most surprised, however, by Hulkenberg's Force India, congratulating the Silverstone based team: "They have made a very good car."
Former third driver Hulkenberg smiled: "I could have gone even faster."
According to Germany's Auto Motor und Sport, Buemi is also impressed with the McLaren.
"It looks good, it has grip -- not quite as much as the Red Bull, but close."
But in trouble, according to former Toro Rosso racer Buemi, is Ferrari.
"Oh dear, that doesn't look so good," he commented after Fernando Alonso passed by. "He's playing with the throttle because there's no traction."
Like Hulkenberg, Sauber's Sergio Perez was also setting the pace on Wednesday, but Buemi reveals that the Mexican was running new soft tyres.
"That distorts the picture, just as the level of fuel does.
"For me, Red Bull is in front, then comes Force India and McLaren," said Buemi. "They are not too far away."