Well, for me it's a combination of factors that really nail the title in place. With my novel, Kiss Me Slowly, the title resonated from the very beginning. I knew the story would be very fast paced, would be about running out of time and love on the run. The fact that there would be no time for indulgences such as lingering kisses prompted the title Kiss Me Slowly--it was ironic, in a way.
With Riptide, that wasn't the case at all. It was originally called Free Fall, but as I wrote and revised, the title simply felt wrong to me. For a short time I called it Notorious, but that's so overdone I hated it from the moment I slapped it up on the header. Then I called it In Too Deep, but thought it could be misconstrued as a porn title. Then it just came to me...Riptide. The definition of riptide is "a stretch of turbulent water in the sea, caused by the meeting of currents or abrupt changes in depth. Also called rip current, a strong current, especially one flowing outwards from the shore, causing disturbance on the surface." Because of the intense nature of this story, which happens to take place on or near the Caribbean Sea at all times, this title slapped me in the face with its rightness.
My next novel is called Reckless Endangerment, but it didn't start out that way either. At first it was called Entangled...which changed to Tattered Angels, which became When Angels Fall and finally Reckless Endangerment perfectly summed it up for me.
And that's the real key here...what resonates with me as the author. I know the story better than anyone and love the characters as if they are real. I owe it to the story to find the title that conveys the tone of the novel. It's not an easy task. A lot rides on the title--marketing, cover design, first impression with the readers--so getting it right feels like a daunting task at times. Think about it...if you don't like the title of either a book or a movie, how likely are you to check it out further? Probably not likely.
As far as what comes first, the characters always tell me their story. They drive it, they shape it...now if only they would introduce themselves politely and say, "this is what I'd like my story to be called, please." If only it were that easy.