Information about the current Matchbox car models that are available can be found at the Mattel website as well as Matchbox Collectibles, Collectors Weekly and Entertainment Earth. A Matchbox checklist is available at Toy Nutz.
Matchbox cars started in 1953 and Hot Wheels started in 1968. Age would tell you that Matchbox might be rarer' cars to collect, however Hot Wheels appears to be more popular. Interesting fact ~ both Hot Wheels and Matchbox are owned by Mattel.
Unfortunately, Matchbox cars are all different scales. The cars are all made to a particular size (no more than 3"). Therefore, a larger car or truck would have to be scaled down more in order to fit the 3" Matchbox size requirement.