Combatants with the most stable reputations
Which characters tend to be ranked more or less the same relative to the hierarchy over time?
I'd say some contenders are:
Peak Luke - was put below the ancient sith a long time ago, but since 2007 he's pretty solidly been at the top of the non-entity mythos.
DE Sidious - except for maybe really early on, he's consistently been put above every other sith.
Vitiate - he hasn't been around for as long, but actually his perceived status as being somewhat below Sidious is pretty consistent, with the exception of his novel version being scaled down, and Valkorion leading some to erroneously put that version over RotS or even RotJ Sidious.
Plagueis - he's always been second, third or fourth among sith.
The Exile - this might be a stretch but people never thought she was super powerful, except for maybe a looong time ago.
I suppose that it's difficult to judge whether a character is moving up or others are moving down. Obi Wan, for example, is perceived to be more powerful relative to the ancient sith than before, but that might just be because people aren't wanking the ancients as much.