Sorry about the long post - but I felt that this should either be answered comrehensively or not at all. So I've written a very long post which I'll put in two messages. Here is the first part:
I’ll give my take on the question here. Note that there are better players out there, but I’ll give my take.
I do think board size matters, and a bunch of civ's do have special needs. Also, characteristics matter. Finally, victory type matters.
Victory Type
Let's start with victory type. Clearly if you are going for a tower victory, you want to go deep, and you will most likely want to get a metamagic node. At this point, then, it becomes a matter of which nodes to build when.
On larger maps there are more mana nodes; this means that we have two ‘pulling’ strategies – both going wide (building lots of different mana) and going deep (building the same mana for free promotions and strionger affinity bonuses) are stronger. Therefore, you have to decide if you are going for the tower victory ASAP and adjust. Note that also (I think) with the Blessing of Amatheon there are more nodes.
Indeed, the second question then is what type of victory you will go for even if you don’t go for a tower victory. Specifically, you have to decide how you will use your magic – to help conquer of help build.
If you are going to conquer, the next question is when you will make the ‘big push’. This could occur more than once. So, for instance, if you are playing on a continents map, you may want to conquer your continent early and then have an overseas conquest, but that may be late in the game. The reason this is important is that you have to decide if you will have just adepts, adepts and some mages, or a full set of archmages
If you are a summoner, then obviously, going for mana that helps summoning is more important. Death mana becomes a good choice because death provides solid summons at all three levels (and allows liches); if you are fighting using mages and adepts, then death is clearly the mana of choice. If you have archmages, then you want a mana with a real nice third level summons. If you go wide and find yourself with archmages, then those genies are real good; that is, genies/metamagic are the ultimate summon for a ‘wide’ strategy. Note that if you are summoning, you want to take strength and spell extension promotions, so the free spell with multiple nodes is useful here.
The next big decision is whether the mages/adepts/ archmages are the key to victory, or they are used to support. And to me, this decision is the single biggest factor.
Say we have an SoD with 50 units – then a support spell like dance of blades can impact 50 units, while a summon, although nice, has far less of an impact; but if you are a summoner and building mages out the wazoo to take the enemy down with minimal losses to permanent units, then you have a totally different strategy.
So, many of my specifics deal with this difference:
Support a large army mana
First level:
Enchantment, magic blade + a happiness, usually my first!
Body, for haste. If you know you won’t have non-alive units, this is probably the best spell – but it is good anyway. All three body spells can be real good.
If you are willing to take the diplo hit, Entropy for rust.
Chaos, dance of blades
Shadow, blur
Sprit, courage (optional). A must in some cases.
If you are on a water map, then air , fair winds, can be very useful.
(This is probably my order). At some point you will want life to sanctify in most cases if you are conquering areas with Hell terrain.
For mages, I like
Air for maelstrom (who doesn’t?)
Body here for regeneration.
Fire - If you go without catapults, we can add fire to bring the city defenses down.
Enchantment - Fire arrows can be nice but I don’t tend to get a lot of archers.
Sun , blinding light – I suspect this is considered a great spell for higher level players – when you are playing on deity and the enemy comes with 742 units in its SoD, being able to blind them to stop them in their tracks can be very useful! Obviously, it is less useful if you have Empyrean as your state religion since you will likely have combat units with this spell.
Shadow – This is especially useful if you are getting through defenses without pounding them down, that is, maelstorm or the equivalent to cause damage and then attack.
Destroy undead is kind of a ‘special’ spell. It is outrageously powerful in certain circumstances, but you need to determine if you will be facing undead.
The third level spells are so powerful I usually don’t choose based on them very often except for specific civ’s or I’ve already decided on death/wraiths or genies.
Builder Mana
Mind is really good! 3% increase in research, wow! And then you put one adept in each city with one FPP and two research, it REALLY ADDS UP!
If you aren’t running city states then think about Law, the 5% reduction in maintenance can be great. If you have overseas colonies it can be especially good.
The happiness from enchantment makes enchantment just a great choice all around when added to its combat benefits, especially early.
Clearly, if you have a lot of desert, I get water for spring probably first. Dessert is terrible!
Builder vs. Combat
This is tough, I usually go for combat, but I have to admit I don’t have a great set of rules.
Other Considerations
I mentioned above that some spells like sanctify are special (as is the second level life spell destroy undead) and the spell courage – sometimes courage is just plain the best spell in the game. Unfortunately, I think these are hard to ‘teach’ a computer.
Another consideration may be the ‘one more for a tower’. Even if you aren’t going for a tower victory, getting a tower can be strategically useful, especially the Tower of Divination which gives a free tech.
Best wishes,
Breunor