I'm going to have to suggest that it depends.
Specifically, it depends on which aspect of the sweater is important to the speaker, or which aspect the speaker thinks the listener would find important. The first adjective in a list is usually the one which the list-maker considers most important.
"Thick, ugly, brown sweater" could be preferred if the speaker wants to emphasize that the sweater makes the wearer look bigger or bulkier (the emphasis is on the external, less personal aspect).
To choose "Ugly, thick, brown sweater" draws more attention to the speaker's opinion of the sweater. This would be important if the speaker wishes to subtly prejudice the reader against the wearer.
1It would depend on whether the thickness contributed to the ugliness, or if it was only the shade of brown that was ugly. – Tᴚoɯɐuo – 2015-07-21T19:29:11.583
1There is a so-called default order to the types of attributive adjective modifiers w.r.t. linear order. And that's probably what you are asking about. But that default order applies when there are no other considerations involved. Context will often easily override that so-called default order. For example, consider: A: "He was wearing his ugly brown sweater." B: "Which one? His thick one or his thin one?" A: "His thick ugly brown sweater." B:"Ah, yes. His thick ugly brown sweater is much uglier than his thin ugly brown sweater." :D – F.E. – 2015-07-22T01:15:37.667