So, since Nubia is supposed to be Egypt's rival, and have some similarities in the types of advantages they get and terrain they like, let's compare them:
UPDATE: With the newly released patch, the Maryannu got a much needed boost (+2 strength, +2 ranged strength, -20 production cost). I have updated the analysis below accordingly. I have used italics to highlight the bits I have changed.
Unique units: Maryannu Chariot Archer versus Pitati Archer
Unlocks with: The Wheel, 105 science into the tree (Maryannu) versus Archery, 75 science into the tree (Pitati). Both these are near the beginning of the research tree, so no major difference in availability.
Cost: 120 production (Maryannu) versus 70 production (Pitati). Even after the patch, this is still a big deal. With Nubia's production bonus for ranged units, they can build about 2.6 units in the time Egypt can build 1.
Strength: 35 ranged, 25 melee versus 30 ranged, 17 melee. The Maryannu has a decent strength edge here, with a ranged strength equal to that of a crossbowman, but earlier in the game, and significantly stronger melee defence. This is made less significant by the fact that Nubians can upgrade their archers more quickly.
Attack range: 2 versus 2
Movement: 2, 4 if starting in open terrain versus 3. So, this one depends on the terrain, but in most cases, I would take a flat 3 over a situational 2 or 4.
Upkeep: 2 gold vs 1 gold. In the base case, you can pay for 2 Nubian archers for each Maryannu. However, if you use the very popular policy which reduces maintenance by 1 gold, the archers have no upkeep, while the chariot archers still cost 1 gold.
Upgrades to: Crossbowman versus Crossbowman
Other:
* Nubian archers synergize with Nubia's UA, giving 50% more experience for ranged units
* Nubian archers upgrade from Slingers, while the chariot archers need to be built from scratch
* Maryannu Chariot Archer replaces the Heavy Chariot, which is a far less expensive melee unit that upgrades to Knight. Losing this early cavalry melee unit may hurt more than what is gained by having access to the Maryannu.
Overall, this is a very clear victory for Nubia.
Unique infrastructure: Sphinx versus Nubian Pyramid
Unlocks with: Craftsmanship, 60 culture into the culture tree versus Masonry, 105 science into the science tree. I'm guessing most of the time, you will get to the Sphinx a bit earlier, although it is not a huge gap.
Base yield: 1 culture, 1 faith versus 1 faith
Additional yields: 2 faith if next to a wonder, 1 culture with Natural history versus 1 yield of any type depending on adjacent districts
Maximum yields: 3 faith, 2 culture versus 1 faith, 6 other yields of various types
Build restrictions: Any land terrain, not adjacent to other Sphinx versus desert terrain, can be adjacent to other pyramid
Other: Pyramid next to city center increases district build bonus from 20% to 40%
This one is less clear. The Sphinx has an advantage in that it is a source of early faith and culture, which is very useful to secure a pantheon and the better forms of government. The pyramid on the other hand, has much higher yield potentials, and I can see it being useful and interesting to build in various spots around the districts in a desert city. It also provides early faith. The district building bonus feels like it is somewhat separate from the tile improvement itself, but it makes the Nubian pyramid a must-build if you have a desert tile next to your city center. Overall, I personally like the pyramid better due to its higher yield potential, but if we don't consider the district build bonus, I think this would be a draw, perhaps a slight win for the Sphinx, since it can be built on any land terrain, and provides that important early game culture.
I'll call this a draw for the tile itself, I'll cover the district bonus separately.
Build-related ability: Iteru versus Kandake of Meroe
Iteru: 15% production bonus for building districts and wonders next to river, can build on floodplains
Kandake of Meroe: 20% production for building districts, 40% if there is a Nubian pyramid next to city center
This is another clear victory for Nubia. Egypt's bonus is either a bit smaller or much smaller, and only applies to to tiles adjacent to a river. There is a small advantage in that it applies to wonders, but in general, this is not the best use for your high-yield floodplains, and only occasionally for other river tiles. Nubia wins.
Other ability: Mediterranean's Bride versus Ta-Seti
Mediterranean's Bride: Plus 4 gold for trade routes to other civilizations. Trade routes to Egypt provide 2 gold, and give 2 food to the trading partner.
Ta-seti: 50% production towards Ranged units, 50% more experience for Ranged units. Plus 1 production for mines over strategic resources, plus 2 gold for mines over luxury or bonus resources.
Once again, Nubia beats Egypt very clearly. I usually prioritize internal trade routes for growth and development. As for incoming trade routes, I have no control over those, and it seems that they will be more beneficial to my trading partners and competing players, than to me. The Egyptian ability may make you a bit of extra gold, but you will have to prioritize foreign trade routes. The Nubian abilities, meanwhile, are universally good. You will always want to improve strategic and luxury resources. Bonus resources you may harvest or improve as you please, but Nubia has an extra incentive to improve them. On its own, I would have preferred this ability over Egypt's, and that is before we get to the part about Ranged units. Ranged units are important throughout the game, and especially in the early game. 50% production is very significant, and 50% experience is also very good. To make it all even better, this synergizes with the excellent unique unit, which can be built in about the same time as regular archers, and will level up quickly. Nubia wins.
So yeah, Nubia just seems vastly superior to Egypt. I know I'm not saying anything controversial here. Egypt is one of the weakest civs in the game, while Nubia, by the looks of it, is going to be one of the most powerful.