I think you've got it the other way around. Pokemon are always used because they're good, so the tier containing the top competitive Pokemon is called "The Overused tier". The element of surprise isn't worth much in the metagame, most people prefer to use proven movesets and Pokemon that have already established themselves as powerful threats, gimmicks are rarely seen, although they can be effective. I really reccomend you stick to using standard Pokemon. Anyhow, here are Smogon's Usage statistics, they start from the most used Pokemon [Ferrothorn] to the lesser used ones.
[Usage Stats]