India is way harder than the Vikings.
All three are difficult ones. However India has a more or less standard strategy. USA is based in luck more or less. Vikings is the most balanced. Moreover, Vikings have more glamorous unique unit.
Mongolia vs Moors:
The greatest military campaign in human history vs the riches of Codroba.
UU:
Keshik vs camel gunner:
Keshik is used, while camel gunner usually not. The
horse riders able to ride for four days with littles sleep beat the moorish hordes every day of the year.
UB:
Ger vs noria:
It's difficult to compare a militaristic building vs an expansionist. These 4 XP points, are gainted too difficult in battle, so it goes to
ger.
UP:
Hords vs irrigation:
Irrigation is too specialised. On the other hand hords give you a big military advantage. The power of the
hords win.
UHC1:
China vs Cordoba:
Cordoban UHC is a matter of luck and the most difficult I supose. The China goal is matter of luck too and difficult, but in a lesser extend. Moreover, controlling china is much more productive than building a strong Codoba.
UHC2:
Razing vs the Andalusian
empire caliphate:
Razing is the obvious option for blood-thirsty players

. However, if we see it with calm, generally razing isn't a good strategy. So this UHC goes to the pitty Caliphate of Cordoba.
UHC3:
The mongol empire vs four people of Cordoba.
These four people are happy to be so far from the
mongol hords... and the moorish civ is too lucky to control both African and European territory so it can survive any kind of perverse mongol human strategy... (Trying to control both North Africa and Iberia is the next mongol game I should play...)
Mongolia: 5
Moors: 1
Genghis Khan beat the moors with ease.
Mongolia!