After losing a siege to a Creative opponent, because his cultural bonus gave him an early 20% defense in an expansion town I got to thinking... Which traits are the most troublesome in your opponents. Also, I think it might help to determine which traits are best overall.

You can vote in the poll, pick as many as you'd like, here is my ranking:

1) Industrious - These people always seem to get the Pyramids if I don't
2) Financial - Generally financial Civs are also more technologically advanced
3) Aggresive - These people seem a little quick to declare war
4) Creative - For the reasons mentioned in the introduction
5) Organized - Not the same impact as financial, also opponents generally have smaller empires
6) Expansive - Not sure, but I bet these people have bigger cities.
7) Philosophical - To my knowledge, an opponent getting a great person does not make it more difficult for you to get one
8) Spiritual - It doesn't bother me to see someone switching Civics

And there you have it, go vote

for quickies, spi is the best trait because they can switch civics on you fast like when you attack them. suddenly a lot of enemy units appear.....

Agressive and Expansive. Crazy dudes with their huge empires and or highly trained armies can be a serious headache.

Financial. I was going to choose Industrious on impulse, because Industrious is very good at the beginning of the game. However, Financial is good from mid to end game, and the opponents that turn into my nemesis in the end game are almost always Financial.

Financial is a real pain. Too many games have ended up with me fighting axross the map to stop a runaway Mansa Musa or Washington.

Industrious often steals wonder from me.

Creative's free land grab is annoying early on and often forces you into a premature war.