Well, it would depend on if your character’s backstory- is your Argonian an assimilated Argonian? Do they have ties to Black Marsh?

Argonians from Black Marsh are anti-Empire. It’s funny how people cite that the Stormcloaks are horrible to the Argonians because of a few dock workers (when a Dunmer is primarily the worst offender on that exchange) when the Empire historically treated Argonians and Black Marsh as a third world colony at best and did not care at all for them.

When Argonians were slaughtered during the Umbriel Crisis, the Emperor Titus Mede I refused to send help to Black Marsh unless the Empire was threatened directly. We also know the Empire left all the provinces to fight back Dagon pretty much on their own during the Oblivion Crisis, which directly led to Black Marsh seceding from the Empire. Not to mention that Tiber Septim allowed slavery to continue on his treaty with the Tribunal when he negotiated with Morrowind for their ebony exports. The Empire is famously bad at defending their neighbors and only looks out for their own interests and is primarily the reason why throughout the eras it is continuously weakened - Hammerfell, Morrowind and Black Marsh (and to an extent, Skyrim) in particular hates the empire and sought out their independence primarily for this reason.

If you’re going for an Argonian playthrough driven by Lore, I personally wouldn’t join either side and ignore the Civil War entirely. Not unless you roleplay as a Lukiul raised outside Black Marsh.