Between the CSA winning the civil war and Nazis winning in WW2, which one is more overused and implausible.
Not sure which is more overused, but a properly done CSA wins TL would be more plausible. Unfortunately, most CSA wins TL are ASB due to uberwanking. The two chief features of these TLs are:
1) The Confederatewank Domino Effect - Any change bigger than Abe Lincoln gets a hangnail inevitably results in Robert E Lee annihilating the Army of the Potomac and seizing Washington DC, Lincoln folding after his brain and spine have been removed, Britain and France become willing to intervene militarily on the Confederacy’s behalf, and the Confederacy is given back every inch of lost territory, plus Kentucky, Missouri, Maryland, Arizona, California, and occasionally Utah and bits of Mexico. If the Confederacy goes after anything in Latin America, the conquest is quick, easy, and permanent.
2) The Confederacy Has No Warts - The large numbers of black and white southerners in the Union Army, the pro-Union guerrillas, the damage to the CSA infrastructure, the massive government debt, and the spiraling inflation magically disappear. Slavery ends almost immediately, usually at the hand of an idealized version of Lee. Confederate politicians show an equanimity about this that makes a bunch of hippies holding hands and singing Kumbayah look like starving feral dogs fighting over a steak. There is no significant dissent on any decision ever made by the Confederate government. Immigrants and free blacks are welcomed with open arms.