INTJ.
Like a master chess player, Littlefinger waits for his opponent to make the wrong move...
It's isn't opportunity as much as it is foresight.
You better believe he's controlling events (see season 1 with the dagger leading to the arrest of Tyrion, maneuvering Lord Stark to investigate the Cersei/Jaime affair which led to the Stark insurrection) but it is so subtle and under-the-radar that you don't notice it until it is too late...he is an amoral monster who has one objective and that makes him a very dangerous person--perhaps the most dangerous man in all of Westeros.
I like this guy.
Littlefinger adapts on the moves of others. He makes his subtle moves and he waits the reaction of others. He made his moves in season 1 and prior to the first book and he waited the chaos that the Starks and Lannisters would bring in Westeros. He wants opportunities so he creates them. As he says, he thrives in chaos. He doesn't have one single plan rather he adapts well in chaos. That's what makes him the most dangerous person in Westeros.
On the other hand, Varys - an INFJ- has a great plan in his mind that he shares with no one. He is the subtle and under-the-radar master chess player. But once you learn his methods you can predict his next moves. With Littlefinger you can expect the unpredictable.