I am sure you all know you can build only 2 national wonders per city and I decided to share some thoughts in the hope of optimizing national wonders per city. This is not as "situational" as you may think as all games need good production, commerce and science cities no matter what type of victory you are aiming for. Not everyone builds national wonders as a priority but it helps a great deal especially if you are industrious and have access to the relevant resources. I am also assuming you play something close to a standard game with at least 6 other civs, on a normal to large map.

Here is a list with their "important" value and abbreviations I will use.

Forbidden Palace.. FP... Reduces maintenance in nearby cities
Globe Theatre..... GT... No unhappiness in that city
Heritage.......... HG... +100% culture
Heroic Epic....... HE... +100% military unit production
Ironworks......... IW... +50% hammers with coal, +50% hammers with iron.
Mt Rushmore....... MR... -25% war weariness in all cities
National Epic..... NE... +100% great person birth rate
Oxford University. OU.. +100% science beakers
Red Cross......... RC... Free medic 1 promotion
Scotland Yard..... SY... Required to train spy
Wall Street....... WS... +100% gold
West Point........ WP... +4 exp points per unit

I will attempt to optimize the wonders for these 2 types of victories: War (Conquest or Domination) and Cultural. Space Race and Diplomatic I have not played yet, maybe an edit will come later if people find this post useful.

War (Conquest or Domination)
You NEED at least one unit production city and by middle to late game you will usually have 2 of these. HE is a must, and wait until IW. Sometimes you will find unhappiness a factor and you can build GT at the expense of IW but then your second powerhouse production city should get that. HW+IW is awesome and by late game you can spit out armors every 1 or 2 turns. WP is an option but I find the units per turn matters a lot more than units with higher XP.

You NEED at least one cash city and as there is a direct relationship between cash and science, the obvious thing to do is to wait for OU then build WS. However this is easier said than done as these come late in the game and your cash city is usually your 2nd or 3rd city that you have hopefully built a lot of cottages around (later on windmills and watermills). As NE comes early in the game you are tempted to build it here, as great person rate helps an awful lot in your commerce city. I find that if you are going for a midgame victory then NE+OU is better, otherwise wait for OU+WS you won't regret it.

The complication with the production and commerce city optimizations as that sometimes your capital is both. Well I think this is due to city mismanagement, it is YOU that made it this way, and you will not get national wonder optimization this way. If your capital is near a few hills and plains then make it a production city, if grassland or river or coast then make it a commerce city then go find a production location near the capital.

TIP: don't forget Literature in the midgame as this gives you HE and NE and these help a great deal. I find going for literature after currency works quite well even if you're warmongering in the early game.

HG is a good one to build near a border as the better the culture around the border the more difficult it is for enemies to reach your cities. MR later on once happiness becomes a problem, does not matter where you build it, but make sure you can build it fairly fast, war weariness tends to creep up on you fast. SY if you really need spies, but I find the aircraft recon method much better for revealing territory.

Cultural
Yes, 3 cities of legendary culture. The trick here is not to throw your best culture wonders at your best culture city, which is usually your capital, due to your free palace. NE is an ok choice for the capital as you can churn out great people to SPREAD around the 3 cities, and wonders. Help your capital with GT. Put HG in one of the other 2, preferably the one that needs it the most. Put IW in the other city to help it to churn out cultural buildings. Don't forget HE to protect your glorious cities! As an aside don't forget religion is very important in the cultural victory, try to found as many as you can. OU is very important for your best science city, so double your science in it and go for those religion and cultural advancements. Don't neglect military defence of course, keep your borders tight. Make friends with as many civs as possible, preferably your neighours, even if you have to convert religion.

Hope this helps. Sorry if there is some similar post somewhere else.

You NEED at least one cash city and as there is a direct relationship between cash and science, the obvious thing to do is to wait for OU then build WS.

I think this is wrong, as commerce is not the same as gold. Wall Street don´t increase your beaker-output.
I prefer to build two commerce-citys, even as warmonger. One for Science with OU and the other with WS for cash (The Cash-City is often a holy city to produce additional gold). In my games one of those citys get often the FP and the other MR.

For a Cultural Victory, I like to put National Epic and Globe Theatre in my main GP city. They both generate Artist points, so you get more of those to help with the Culture boost and with the Globe, you can grow it as much as you are able to and set a lot of artist specialists. Also, I build whatever Wonders generate Artist points in that city and any other Wonders in one of the other two cities.

If you have a lot of Artists, you don't have to worry about all three cities keeping pace with each other, since you can just culture bomb at the end to bring the second two up to the 50,000 mark.

I prefer to build two commerce-citys, even as warmonger. One for Science with OU and the other with WS for cash (The Cash-City is often a holy city to produce additional gold). In my games one of those citys get often the FP and the other MR.


Does it always have to be the Holy City? Or can is just be the highest Cash producing city?

HW+IW is awesome and by late game you can spit out armors every 1 or 2 turns. WP is an option but I find the units per turn matters a lot more than units with higher XP.
VERY bad choice. As you note, you'll need at least two production cities anyway. Which means you don't get any more units per turn by doing this (remember, the bonuses add, they do NOT multiply). HE+WP in one city and IW (possibly with RC) in a second city gets you just as many units, and the units you get are superior. Beyond that, you can divert the IW to wonder-building without giving up all benefits from the HE. It's a win-win situation. The only situation in which you could possibly justify HE+IW is if you have a single city with much higher base hammers than any other (i.e. you have only one production city). And then it's questionable.

Always remember, the key to effective specialization is synergy. You want combinations that, when put together, produce a greater benefit than they do seperately. HE+WP is a perfect example - WP makes the HE more effective because the units it produces are better. HE makes WP more effective because more units get the bonus. IW+HE is a perfect example of NOT having synergy - you gain exactly the same benefit if they're seperate as if they're together.

You NEED at least one cash city and as there is a direct relationship between cash and science, the obvious thing to do is to wait for OU then build WS. However this is easier said than done as these come late in the game and your cash city is usually your 2nd or 3rd city that you have hopefully built a lot of cottages around (later on windmills and watermills). As NE comes early in the game you are tempted to build it here, as great person rate helps an awful lot in your commerce city. I find that if you are going for a midgame victory then NE+OU is better, otherwise wait for OU+WS you won't regret it.
Again, very poor choices. NE doesn't help a cottage-based commerce city at all. If you're building a research or cash city out of specialists, then NE can be a good choice since you've effectively made it a GP farm too. Otherwise, bad idea.

Also, WS+OU is only a good combo if you're funding your civ off taxes. Which is frequently the case, but certainly not always. If you're funding your civ off shrine income, WS should be in your holy city since it will provide NO benefit to a commerce city if you're running 100% science.

I'll also note that petey makes an excellent point. NE+GT is a perfect combo for a GP farm.

Does it always have to be the Holy City? Or can is just be the highest Cash producing city?

The WS should be build in the city with the highest gold-production. This City is often a holy city, because a holy shrine produces a lot of gold, when the religion is spread over the world.