So, let's compare the remaining units.
Camel archer (7) - Replaces the Knight. They have 3 less strength but can do the move foward, shoot, and retreat bit, with more effect and less strength then the DLC Mandys. Personally? I don't really like them. In general, more ranged units is bad, simply because when they upgrade to Cavalry, half of their promotions become useless. I predict they are next to cut.
Mandekalu Cavalry (31) - Same strength as the Knight, but they get a massive +33% bonus against cities instead of a -25% cut. Chivalry is harder to RA block then Steel, but more useful too, given that the two techs right under it - Economy and Education - are very important builder techs. Combined with the Songhai bonus for pillaging cities, you'll want to build a large Mandekalu army, a couple Longswords and/or Pikes, and then rush down cities like no tommorow. Upgraded Cav fare better against cities, actually, as well, but the ability is really corroded by the later negatives. I predict 4th.
Cossack 11 - Hmm. Cossacks get a bonus against wounded units. Can't say much about them b/c I haven't played with them significantly, but their UA doesn't seem like such a deal breaker in a pitched battle. Still, they must be monstrous at cleanup and sniping the wounded. I predict second-to-next to cut.
Immortal 20 - Get 2 heal in outside territory, 4 in friendly, which means that, as long as they're not facing down a teched-down or walled-out capital, they can camp down cities and shug off whatever the enemy throws down. Not an aggressive unit overall, but great for defending against over-militaristic AIs, esp. on Diety. Also have 1 more strength. I predict 8th.
Legion 20 - Get 2 more damage and can build roads. Classical rush with 5 Legions, nuff said. Like Swordsmen but better basically. I predict 6th.
Foreign Legion 25 - Aggressive Riflemen with a bonus on enemy territory. War war war, basically. Imperialism ftw! I predict 6th.
Longbowman 24 - Get 1 more range. Helpful for sniping units down, defending your territory. Insures they won't get run over by Knights without having their fair share. I predict 7th.
Naresuan elephant 28 - Super heavy Seige engines. I remember MadDjinn pointing out somewhere that it was mathematically pointless to upgrade them to Cavalry.

They have one less move but 4 more attack then Knights, AND get a 100% bonus against other mounted units. Almost break even with Pikes, actually. I predict 3rd.
Chu-Ko-Nu 36 - Double fire Crossbows that can thus actually attack cities with some affect, but are much frailer to direct attack. Also good at finishing critically wounded units. Build a whole bunch of them and enslave the world. Biggest con is the fact that their promotion path goes through the Ranged promos, which, once upgraded, are useless. I predict 5th.
Samurai 34 - Get Great Generals at 3x speed, also start with Shock I. With an Armory, that means you can get STARTING Samuri with Shock I, Shock II, and Shock III right out of the gate. The jump to 60 experience isn't so bad, another 6 battles I think, but jumping all the way to 100 is hard, something like 8 battles on top of that. That basically means that Samurai get March/Blitz a faster then regular Long-swords. Plus, they are in that critical area when you just have enough resources to start uber-warmongering. Plus, they form the backbone of your army for the rest of your game. Plus the Japanese UA pumps them up even more. Methinks, 2nd.
Janissary 40 - They heal fully when they chew down on another unit. They would be overpowered, 'xcept for the fact that the rest of the Ottomans is totally worthless

Jannies can smash through attacks again and again, without having to heal. The tradeoff is of course the fact that you have to hard-build them, because those pesky Musketmen don't upgrade from anything. Shucks. Obviously 1st.
Now to sit back and see how my predictions roll out.
