Dont mix a serra with a pygo. WILL NOT WORK.
As far as the most aggressive its hard to say. Actually what is aggressive? Is aggressive to you in the way a fish eats its food or is it the way the fish interacts with you?
In my experience S. Maculatus (Gold/purple spilo, and no I am not talking about S. Sanchezi even though they are also labeled purple spilos and no i do not mean true S. Spilopleurea as they are very rare in the hobby and most "spilos" are Macs) are the most aggressive when it comes to chasing fingers and stuff.
Another thing to remember is give your fish time. My 8" Mac was a pussy for like the first three months I had him. Now he is an absolute beast and you cant walk by his tnak with out him trying to kill you!