Titus and Philemon are similar, and very different, letters.
They are similar because they are both short letters to individuals (rather than the letters Paul wrote to churches). Titus is a congregational leader, and Philemon may also have been a church leader, but he also appears to be a wealthy Christian individual. But for all of their similarities, the two letters seem very different.
The letter to Titus seems less personal, more concerned with church order and everyone's behavior. Paul does not want the congregation members to give offense in the community, so advices masters and slaves, older men and older women, and advices the congregation members to live in peace in the community as well. Paul seems to concerned that no one make waves -- he doesn't seem like the same person that once healed a slave girl who was possessed by a demon, because she was following them around and shouting. He doesn't seem like the same person who made waves everywhere he went, until people say, "These people who have turned the world upside down have come here also!"
But something is going on in the world now -- and Paul is concerned that the community not make waves.
Then there is the letter to Philemon. What I love about this letter is that, just like all good personal letters, we don't know exactly what is going on, because we only have one side of the conversation. But we know that Paul's letter to Philemon has to do with one of Philemon's slaves, Onesimus. Onesimus may have run away, or he may have been sent away, but Paul has met him, and now he is sending him back to Philemon. In the meantime, Onesimus has become a believer, and when Paul sends him back to his master, he asks him to consider Onesimus not simply as a slave, but as a brother in Christ.
There's more going on, of course, but this very short letter is a window not just into an aspect of the first century world and church, but a glimpse of the apostle Paul: charming, passionate and persuasive. And witty -- the word "Onesimus" means "useful."