3 - Charitable Missions: Influence boosts from Gold gifts to City-States are increased by 30%.
Not yet tried this one, but if you were wanting to get City State allies, the Patronage tree is quite enough IMHO. There are also plenty of CS challenges which bring about plenty of influence boosts.
5 - Evangelism: Missionaries' Spread Religion action erodes existing pressure from other religions.
People say this is situational... IMO this is a must for Cultural Victories. Getting your religion into other civs gives you a tourism bonus with said civ, and by eroding other religions, you're essentially turning your missionaries into pseudo-Great Prophets. This stacks very nicely with the Great Mosque of Djenne and Tithe - since when is more gold situational?
1 - Heathen Conversion: Missionaries convert adjacent barbarians to this civilization.
By the time you've gotten to the reformation belief policy, your military should be far more advanced than that of barbarians, and then it will only be useful if you've got raging barbarians turned on and Shaka breathing down your neck.
3 - Jesuit Education: May build Universities, Public Schools, and Research Labs with Faith.
You're best off spending your faith on missionaries and Tithing your way through. The only time I've found this remotely useful is when I have a jungle heavy city with low production and the university is required. By the time Public Schools and Research Labs come around, I have enough cash to buy however many I want.
4 - Religious Fervor: Use Faith to purchase Industrial Era (and later) land units.
I've not used this, but I can see this being very useful in late game Domination. I do feel that saving your faith for late game scientists is the better use for faith at this point.
4 - Sacred Sites: All buildings purchased with Faith provide 2 Tourism each.
Useful for when Ideologies come about. With a fairly wide empire, and 1-3 faith buildings in each city, you can have most civs at ~60% influence by the time they choose their ideology. Going super wide with 2-3 faith buildings can have you the game won in very fast times, that is, if no-one DOW's you.
2 - The Glory of God: Use Faith to purchase any type of Great Person starting in Industrial Era.
Only useful if you don't generate the Culture points necessary to get the required trees. Science victories should have Tradition and Rationalism filled already, so GE and GS are not a problem. GG and GAdmirals are only required if you are at war, and if you are, these will be generated fast enough. If they're not, then your opposition is not strong enough for you to require one. For culture victories, GW, GA and GM grow very fast regardless whether or not you take the right tree for it. That said, managing your policies negates any use of this belief.
1 - Underground Sect: Your spies exert religious pressure on the cities they occupy.
Not nearly as powerful as other faith exerting/protecting beliefs on this list.
4 - Unity of the Prophets: Inquisitors and Prophets reduce this religion's presence by half (instead of eliminating it).
I have not tried this one yet (too used to Evangelism), but from what I've seen, this is really good if you come up against Great Prophet spammers. Remember, it not only protects your own cities, but whichever city your religion is in. You can keep your religion in every city on the map, which means this stacks very nicely with Tithe.
With most of these, it's not worth spending an entire policy trees worth of culture getting when you can be getting better bonuses from other trees. E.g. Rationalism > Jesuit Education. It also means you can finish another tree with more useful aspects elsewhere to open up another Great Person which may not necessarily be essential for victory (hence negating The Glory of God). And surely the Honor tree is more useful than Heathen Conversion?
