One of my characters was evil and joined the DB and thus also the empire. In the end i deleted him as i simply couldnt stand him.
The empire is a huge NONO for me because of many many reasons here are but a few:
-Has lost all legitimacy due to the fact that they have no dragonborn emperor anymore (thus an imposter rules). As said in the prophecy "when misrule takes place".
-They torture people left and right, Helgen which is a small military camp has a whole dungeon for torture. Here they maim, starve, murder any and all that dare question them or the thalmor.
-They have become puppets to a regime (the thalmor) that abducts anyone (men, women, children) and torture them to death for simply not sharing their faith. The empire openly protects this.
-Jarl Balgruuf admits that the Empire got alot of gold for signing the white gold concordat, making all men slaves to the thalmors whims. The nobles in the empire endless greed and war fatigue sold everything out after a major victory. The thalmor makes wars with all weapons and greed and fear finally won them the war even after their defeat.
-The empire abandoned Hammerfell that later, proved itself right to continue the fight and thus the empire wrong. With sacrifice the thalmor would be defeated.
-The empire would rather start a civil war than leave Skyrim, even though they know that this war will benefit the thalmor. Their greed and lust for power is simply to great.
-The empire wants to execute the main character for having done absolutely nothing wrong. Just being in the general area as the stormcloaks is enough to be executed. The general for the enitire area is present and he does not care one bit. He has probably murdered thousands of innocents by this time anyways...
-If you do help the empire in the beginning and save Hadvars life. He says im sure that general Tullius will give you a pardon (a pardon for what?? for being in the wrong place at the wrong time, im so sorry)
-The empire is clearly racist as it has chosen to forbid a whole culture and religion.
-The ruling class of the empire has strong ties to corruption and crime (the thieves guild, maven black briar etc). In fact it so common and widespread that this how the ruling is now accepted to be done.
As for the stormcloaks:
-They are led by a warhero that is so broken and torn from the civil war that his righthand man must convince him to give orders. He has been sent to the bloodiest of wars, then being betrayed by a peace, tortured til breaking by the thalmor, imprisoned. Yet he picks up the pieces and cannot stop fighting. As he says in his private conversation with Galmar:
-I fight so that all the fighting I have allready done should not be for nothing, I fight for the dying friends ive held in my arms so that their sacrifices should not be forgotten. I fight because i returned home to place full of familiar faces that now were strangers (ie having abandoned their faith, the empire, the truth, honor). I fight because I must.
-Ulfric hides the fact that the thalmor broke him and still continues to prepare war with them. As seen after a stormcloak victory, the smiths in solitude are now ordered to produce as much weapons as during the bloody civil war. Because a new war is coming.
- Ulfric hesitates to send in his army vs whiterun. He does not want more death. But the alternative is stagnation and thus profiting the thalmor. He is a weak leader and the dovahkiin would have been better. I do however feel pity for this tortured old veteran that is so sick of bloodshed yet wills himself to continue, even if it takes Galmars strong heart and voice to push him forward.
- The courage the general stormcloak shows is amazing, as seen in the opening scene. They sacrifice themselves to persecution, torture and death. Simply for freedom. Freedom from the thalmor, religious and political freedom from an empire that tax and punish them but give nothinh in return.
- The stormcloaks allow the dunmer refugees to live within the walled city, in houses after the amazing racism that the dunmer shoved on all others. The dunmer only complain that their caravans are not protected. Yet it is clearly told that Ulfric cant even protect the city from a massmurderer (that goes after nord women) due to the fact that he needs his guards in the war. Yet he is a nazi for not protecting the dunmer on the open roads....
-Anyone is allowed to join the stormcloaks and many do. Ive met redguards, dunmer, high elves on their way to join ulfric and the high elf merchant in windhelm clearly states that after gaining the stormcloaks trust they are awesome allies.
-Ulfric is slandered by the empire by pure lies, the bear of markarth is held as an objective text on the forums yet is cleary written as propagande by the empire, for the empire. Bethesda clearly rights this out when you read the author. But it does not stop there, they say Ulfric murdered the high king yet it is made clear that it was a challenge that the high king accepted. A challenge that nords accept to be lawful and true. And ulfric even admits he didnt want to do this, he is sorry for the high king but he had no choice in his mind. He was a puppet king of the empire and the thalmor and he couldnt protect skyrim anymore than he could protect himself. The high king even respected Ulfric greatly but Ulfric knew that he had no choice but challenge him or see his people destroyed by a puppet ruler that wouldnt even realise it. Protected in his palace, entertained by his queen.
To me the choice of what faction to join as all races other than a rped thalmor joins the stormcloaks (or unless very evil)
-Bosmer (the thalmor do purges on them, this is nazi stuff) no way that they can support an empire that helps the thalmor abduct, torture etc. Same goes for dunmer, redguard.
-The very last thing i will add is this. If you do join the empire then the broken old warhero Ulfric asks that you kill him as you are dragonborn (the right to rule, chosen etc). He finds comfort in any little thing and even though he is a plagued old man i pitied him there. After killing him you find him in the nords heaven. Showing what kind of a man he was...despite all his flaws and all that he suffered.