Personally.. I have to give my vote to the argonians. High immunity to disease and poison. Physically tough in their capacity to take pain and dish it out (with claws and teeth). They have great stamina. They are definitely highly intelligent and have a calm and calculating nature. They are good swimmers and breath under water giving them high advantages in water terrains. Their scales give them a kind of natural camouflage which also gives them a natural edge,

They also are the only Province that forced the Dremora to actually close the oblivion gates and retreat because when the gates opened in Argonia, instead of defending. The Argonians invaded the Oblivion gates and won.

Plus if they wanted to, they could create an entire nation underwater and be impossible to attack while still giving the argonians free reign to attack anyone else

So.. who do you think in Tamriel holds the most power militarily? (At current time in Elder scrolls lore. Fourth Era)

The Dominion, because Bosmer, Khajitt, and Goblins can be used as Nordfodder.

The Empire can be the Second, but the Imperial Legion has a Political Weakness by being under the screws of the Elder Council.

Nords are Third, Redgaurds are Fourth.

Orsimer are still recovering from the last Razing of Orsinium.

Bretons have too many Politics to field a unified Army.

Argonians are powerful, but only in defence of Argonia.

The Bosmer Wild Hunt has been shown to have a weakness to a strong Army, King Borgas has all of his limbs.

Eh, the Argonians at home, sure, but that's mostly due to the fact that trying to run armies anywhere within the center of Black Marsh svcks, and you're more likely to lose men from the local flora and fauna as opposed to any seriously militant opposition. I think that's a sever overestimation as to what the Argonians are capable of. They'd seriously need to start producing and creating some serious industry that can branch outside of Blackmarsh if they wanted to take the fight anywhere, never mind the fact that the Hist isn't going to hop them up on sap every time they want to fight. Remember, the Oblivion Crisis was a case of extreme circumstances. There's also the fact that theyopted to make hit and run passes at the Dunmer after they were weakened, and were pushed back the moment the Dunmer finally reorganized. They probably didn't want to go in as conquerors, but the Argonians by themselves generally don't go for any military expeditions, so its not unreasonable that it'd be disorganized while favoring guerrilla warfare at home.

Overall, its a tossup between the Dominion and the Empire at this point, since both sides have amongst the largest military might to muster for the time being. Empire is sorta in shambles though, and its hard to tell how much the Dominions strength at the moment is part misinformation and political chest pounding.

As for personal preferences, the Crowns and Forebears united aren't a force to mess around with. Nords neither, provided they're motivated enough.

Hard to say, I would probably have to say the Dominion in first place but it is a sort of tentative position. Mostly I feel that way based off of the history and current affairs but don't have a lot of specifics to really say. The Argonians may very well have a strong military, not a lot of detailed information is available about a unified military structure from them at the moment. Then the Empire I would say, but that is also partially based off of my 'canon' for Skyrim.