Spike is really the character through whose eyes we discover the child like wonderment of Transformers. His friendship with the Autobots was always our strongest link to understanding what they were all about. Sam, well, he introduced the moviegoing world to Transformers, but in a significantly less "childlike wonderment" kind of way. I sort of feel that if Sam had been more like Spike, more fascinated and less scared, maybe we'd like him more.
I don't mind Sam at all, but Spike wins in my book. Only a few people can pull off the yellow galoshes look.