Not necessarily the best, however I always thought DC was more than capable of winning a WDC. Lets not forget he had the beating of Hakkinen until he let him win in Jerez in 1997 and then again pulled over in Melbourne the following race. Always a confidence driver sadly.
My main argument however goes for Heinz-Harald Frentzen. One of the 3 young German-speaking drivers to come up through F3 etc. including Wednlinger and of course Schumacher.
While his team-mate at Williams in 1997 had significantly less F1 experience, Villenueve did have the big-race experience and while he got a victory and a joint-pole in 1997 Frentzen wasn’t really up there with JV and Schumacher.
However in 1999 he managed to put a complete independent which didn’t have “factory” backing in a credible position to challenge for the WDC title. Unlike his more senior team-mate Damon Hill who managed a 4th at San Marino, a race in which H-HF didn’t finish.
Also I always felt sorry for him as not only did Schumacher go from being his equal in German F3 to undisputed statistical F1 champion, Schumacher also stole his girlfriend! I’m not sure if he actually “stole” her, but it would fit with the generally-perceived mid-1990′s Schumacher personality…