Ink has been spilled about domains elsewhere, particularly from a mechanics point of view. As I understand domains, they serve two main functions: customizing your abilities, and narrowing down your relation to the deity/forces/etc.
Mechanically speaking, domains are the easiest way to give your cleric unique abilities and specalized spells without dipping into archetypes and such. A cleric with Animal and Plant has taken serious steps in the Druid direction--gets an animal companion, nature-oriented utility spells, and manipulates the battlefield using plant life, while Fire gives you some blasting power, and Void or Feather let you fly!
Sun is great if you're interested in fighting undead, and doing so in flashy style. Travel gives you teleportation, which is otherwise a Sorceror/Wizard thing. Void gives you flying and planar binding spells, both of which are really powerful. Law has useful abilities (Protection maybe too), but I'm less interested in them because most of their spells are already on your list--so still useful if you like those spells, and more spells is always good, but it can be fun to have access to some different spells too. So I would say Travel and Void are the most powerful choices, with Sun an option if you're going to deal with undead or go on a crusade.
Roleplay-wise, what aspects of your god's teachings are most important to you? In our world, a follower of Odin who emphasized his role as king of the Aesir (e.g. Nobility and Glory, maybe) might have a very different spirituality than one who emphasized his role as magician and seeker of hidden knowledge (e.g. Knowledge and Magic). Or look at the different forms of the Virgin Mary in the Catholic Church, each of which have their own iconography and even dedicated orders--Mother of God, Mother of Sorrows, Queen of the World, Star of the Sea--all of these are very different.
It seems like your character wouldn't emphasize Law. Travel could be good, because the character had a conversion experience while traveling, and presumably plans to travel more. Void could be interesting if you take the "Dark Night of the Soul" kind of approach, or if you have reason to be interested in summoning beings from beyond our ordinary world with the planar binding spells. Sun could work if you live in the desert, or if you want to pair it with Void in a sort of cosmic creation-destruction or emptiness-meaning sort of pairing.