I generally find 3 different types:
1) The anime doesn't bother with episode titles
2) The anime uses 1 or 2 words in the title
3) The rest

Typically, those with 1 or 2 words, generally don't relate too much to the content of the episode, thus the aim is more to probably evoke some emotional thought (or act as some symbol).

What do you think are the best?  Do you really pay any attention to the titles?  Do you think they have an effect on you?