Board Thread:General Mod Discussion/@comment-2001:569:7528:CB00:BCE2:1603:1B9E:179F-20170704202241/@comment-29773086-20170704234718

Equites wrote: @Doge

Yeah, it really just depends on your personal perception. They were almost certainly in incorporeal form before they were bound to Arda, and what form they most often took afterwards is unknown. I find that it helps to envision their forms as their "clothes," in that they change forms to meet their fancies. Thus, like us, many Valar often wore the same or similar "clothes". Their forms could also be driven by context. Ulmo, for instance, took the form of an awe inspiring lord of the Sea when he met with Tuor. Keep in mind that this is all my opinion.

That's all pretty much confirmed by the Valaquenta, except that some Valar change or take forms less often than others, and some of their forms are described.