The three main settings in Uncle Tom's Cabin are the Shelby farm in Kentucky, the St. Clare household in New Orleans, and Simon Legree's cotton plantation. Through these settings, Harriet Beecher Stowe is able to explore a range of possible slave experiences from the best to the worst.
As the novel opens, Tom is in one of the best situations a slave could find himself in. He has kind owners, especially in Mrs. Shelby, a compassionate Christian woman who care about her slaves as human beings. Tom lives in his own tidy cabin with his wife and children and is treated with dignity.
After he is sold, Tom ends up in a more middle-of-the-road situation. As was common for slaves, he is separated from his family, but his new owner, Mr. St. Clare, is a decent master. He allows the household to muddle along in an overly chaotic way, but he also kindly indulges some of the whims of the slaves, understanding that they are human beings who don't deserve to be cruelly crushed. He knows slavery is a deeply evil institution but doesn't know how to extricate himself from it. He even agrees to grant Tom his freedom, but he dies before he can do so.
When sold to Simon Legree, Tom has the worst possible slave experience. He finds himself in an isolated setting where gross abuse of slaves is the norm. Legree finds it cheaper to work slaves to death and replace them than to treat them humanely. He ultimately beats Tom to death.