See that's 3 names for the same thing. I wanna learn fighting games, not a language!
Spike/Timmy/Johnny is just a Magic thing, it's harder to use for fighting games. No one really should be using for fighting games, we were just doing it for the sake of discussion here. It's not like you can construct your own character in a fighting game, it can really only apply to MVC3 where you can construct your own teams.
Tier whore I never liked because it gives a bad connotation to players who pick the best in order to increase their chances of winning. It sounds too much like scrub talk and one of those mind games/OSes that pro players like to use to belittle each other.
Tier enthusiast is more tasteful.
What's this Johnny Spike stuff
Some guy who plays Magic the Gathering categorized the player base falling into 3 archetypes:
Timmy: Casual player, gets impressed by something cool and tries to use that to win. Doesn't care if it's actually good or not. In fighting games this would be a low tier hero (though not necessarily).
Spike: aka Tier enthusiast, picks to win etc.
Johnny: Some what in between Timmy and Spike. Obviously plays to win but tries to do so on his term and playstyle.