The 2006 Renault was the best car. But when the Michelins were found to be illegal (again, this happened in 2003 as well), the Ferrari was the best for the last 4 races. Schumacher then lost out for rare mechanical problems.
In 2005 (on said rule-bending Michelins) the McLaren was indeed the better car and Kimi lost out because of it. I need to go and refind the report about Ferrari testing their 2005 car on the 2005 Michelins in 2008 and either Badoer or Gene set a lap time over a second faster than Schumacher managed with the same car on Bridgestone tyres at Imola during the season. So technically, the Ferrari was the best car in 2005 lol