Travel is the most generally applicable of the powerful domains and that probably wins it the title of "most powerful" but I hesitate to recommend it universally. It depends on what the player in question wants to do and/or what they know about the nature of the campaign. Some other domains like Souls, Liberation and Sun are stupidly powerful if their niche comes up. While I generally try to encourage players to avoid considering themselves primary healers, the Healing domain is very strong at what it does as well.
Travel is probably at its strongest when the cleric is wearing heavy armor or non-mithral medium armor (going from 20' to 30' is way more important than going from 30' to 40') or when the party has insufficient mobility support from the arcane classes. If a party Wizard or Sorcerer has Fly & Dimension Door covered, it could end up looking somewhat anemic.
Broadly speaking, I try to find one domain that has good features (and hoepfully good spells) and one domain that has good spells (and hopefully good features).
Here's a list of good domains to look at off the top of my head: (* denotes that the domain assumes some non-trivial investment in Wisdom, + assumes a battle cleric build that can actually hit enemies)
Defense subdomain - most of the Protection domain sucks but having Shield & Barkskin as domain spells is phenomenal
Love subdomain* - the Adoration power is great and you pick up Heroism
Plant domain - more Barkskin. I almost put an * on this one to take better advantage of Entangle, but the domain powers are better for battle clerics. Take a look at the Growth subdomain as well.
Good domain - Touch of Good is a crazy ally buff
Healing domain - cure spells become actually good after you get Empowered heals. Still not good enough to do every round, but it doesn't feel like a waste of an action to do Cure Moderate Wounds anymore.
Luck domain - another crazy ally buff
Travel domain - discussed thoroughly in the rest of the thread
Frenzy subdomain+ - the correctly done version of both the Destruction domain and the Strength domain
Fire domain* - If you don't have an evoker of some sort, Burning Hands and Fireball will help to control swarms. If you do have an evoker-type around, throwing your Fireball at the same location they did can finish off many enemy groups.