The problem is that unlike the old South, where there was a thoroughly Southern identity, no such state exists today. Being generous, you might find a state where secession enjoys support from 60% of the population. Secession simply isn’t possible when 4 out of every 10 people are against it. The type of majority that would be needed does not exist.
Secession is a slow moldering burn that last a long time. Then all of a sudden it flares up like wildfire when the yoke is thrown off and freedom is felt cursing through rebel veins. You are alive for the first time.
I would say Texas would be the most likely one and if a movement started to gather steam then many would move there and swell the ranks of the movement and I might just be one of them.