the general best item

Definitely Odin's set ( I think the one You name Zeus), but Keel is also good because is allows great survivability dus to defense and HP regen. However Paladin's is easiest to get, and it still grants a lot of HP.

Unlike previous games like EW4 or Three Kingdoms, items are not generally restricted to a certain unit type. However, I do recommend the following:
Paladin's set is best for Archers, ( Nobunaga, Nelson or Catherine) since they have very low health compared to other units and the HP regen and bonus HP is very helpful.

Keel's set is amazingly good for suicidal breakthroughs or just for defense. Top choice for infantry (Alexander and Caesar).

Titan's set is good for artillery( mainly Napoleon, perhaps Li Shimin) since the bonus attack comes in handy and it is terrible at close combat (the set)( low HP, low defense, no HP regen, inferior hit and evasion etc.)

Odin's set is the best all-around and you should give it to your best general. Those who can deal a lot of damage are the best for this one ( Cavalry like Saladin,  Attila maybe Suleiman and Li Shimin If he gets Fire Dragon ability on his 6 star)

I put Paladin on Attila because that 20% initial rage allows him to keep the cavalry commander buff up forever.
I plan to put Titan on Blucher hoping that bonus rage regen will help him spam armor master buff.
With 4 cavalry generals and 2 buffs up at all time, I am happy. Oh wait... I don't have the medals to buy Blucher and those items yet.

4 cavalary general team sounds challeging. However, i like more the combination of general type. Especially strong archers are great

I added this table to 1st page of data file, THXN!

If you have IAP generals:

Odin: Washington
Paladin: Caesar
Keel: Genghis Khan
Titan: Napoleon

If you don't have IAP generals:

Odin: Nobunaga or Nelson
Paladin: Caesar
Keel: Attila, Suleiman or Blucher (it depends which one do you prefer)
Titan: Li Shimin

As you wish.

Reasoning:

Archers need high HP (or defense, or both), so Odin or Keel.
Caesar must have Rage Regeneration so, Paladin or Titan.
Cavalry needs defense and/or HP Regeneration, so Paladin or Keel.
Artillery needs high attack, so Titan or Odin.

Washington has Logistics, so he can regain 12% of his HP by destroying something. If he has more HP, he can regain more from that 12%.
He has the best attack in the entire game, it makes sense to improve it over 1000 to destroy most units in one hit, and regain HP easily.
Odin has the most Hit points from all sets so, if Washington attacks something it will be attacked. There is nothing worse than a "miss" in a crucial situation with your best general.
If you don't have Washington, other archer units as Nobunaga or Nelson are the closest pick. They have low HP, so +900 comes handy, and +280 on attack makes them also or near one-hit-destroy generals. That is very useful for Nelson, as he has a range of 2-3 just like artillery.

Caesar's most valuable skill is Cure Master. You have to make sure, that he can use it every 3 turns. Only Paladin and Titan give more Rage, but Titan is not meant to be a close-combat set (low HP, low Defense compared to other sets). So, Caesar has to have Paladin.

Keel has the most Defense (245), and the most HP regeneration. Only Genghis Khan has no HP Regeneration out of the 4 best generals of the game, so it must be compromised. Also, cavalry is vulnerable against archers, so the increased defense is the best option, since Genghis has incredible high HP.
Because of the high Defense, the Keel set is optimal for cavalry units. Only if you use Blucher instead of Attila or Suleiman as your main cavalry general can you consider Odin, due to more HP, and Blucher has Plunder at elite troop.

Titan is a set made for artillery. It has the second highest attack (250) which is handy, since artillery has lower attack. It gives the most Evasion, (415) which is enough to make sure Napoleon does not get hit by common units.
Movement is also "just" 14, so it isn't the front unit in automatic battles. Since rage fills slower for artillery units (it's not a front unit), the +20% Rage Regeneration makes up for that.
If you don't have Napoleon, Li Shimin is the best choice, for the same reasons.
Plunder (Napoleon) and Logistics (Li Shimin) is not much affected by the Titan set, but artillery has the most HP at stock, so it is not that important as other stats. Also, Napoleon regains 552 HP at elite troop level 60, by destroying something, and Li Shimin regains 496. That’s fairly enough, I assume.

Summary:

Archers are best to go with Odin. If you use Blucher as cavalry you can give him Odin, and the archer general the Keel one.
Caesar needs Paladin, due to Rage Regeneration, and Titan doesn’t fit him.
Titan is the best choice for artillery, due to Odin is better on a general with more impact, like the archers.
Keel is best for the cavalry, due to high defense, and HP Regeneration.