Aguero is all those things, explosive, quick and skillful but so is Tevez with the addition of being strong and hardworking, it doesn't matter how magical Aguero seems at times until he can do it consistently and fit into City's formation (he wouldn't work as a 1 in their 4-5-1) he simply isn't as effective as Tevez, I know you don't like to look at things like efficiency and just go with what you see but Tevez improves City more than Aguero would do.
A front-line of both of them could be fricking scary though, best hope Aguero gets a good look at what Manchester is like and decides against it.