The map and victory conditions are important.
As someone else pointed out, the Pyramids and SunTzu only apply
to the continent where they are built. I find that after I've invaded
another large island/continent, I really wish I had granaries or barracks
over there, to bulk up my forces and conquer the rest of the other
land mass. It's a lot easier to cash-rush cavs and tanks locally than
to build them in the core, get them onto ships, and drive them to the front.
Leo's allows upgrades *everywhere*, as long as you've got barracks
and the cash
On a pangea map, the above comments don't apply. On archipelago maps,
the "continents" for the Pyramids and SunTzu are even smaller.
It seems to me that the victory condition is also important. If I'm going
for a cultural or diplo victory, I want my cities to grow and spread their
cultural radii -- Leo's or SunTzu would be less useful. If I want a conquest
or domination win, producing all veteran units is doubly good.
Vets are more likely to win battles, and are one step closer to elite,
which leads to great leader formation.
And then there is the aspect of wonder denial -- keeping a rival civ
from getting one of these wonders, and becoming a KAI. From reading
the posts of higher level players, this latter seems to be a low priority, though.