My brother thinks a ruckus is more violent than a rumpus. I think most people normally only use one word or the other for any disturbance/commotion.
Apologies if this looks a bit like a "vote" type of question, but who's right?
In American English I'd agree with the connotation of ruckus being undesirable. I know that many people had, and some still have, a rumpus room, but I have never encountered anyone with a ruckus room.
[Edit] In looking for outside confirmation of my own experience, I see that rumpus room also goes by ruckus room.
I still hold that I've never heard that usage in Western US usage, nor in any reading regarding Architecture or home building.
Both rumpus and ruckus (along with fracas and ruction) are nonce words for, as you say, "any disturbance/commotion". So different people can use them in ways that sound right to them.
However, as we demonstrate here continually, any given thing may, or may not, sound "right" to any given person.
This is where phonosemantics comes in. There is a phonosemantic "meaning" (the quotes indicate it's not quite the same thing of "meaning" as dictionary "meaning") around simplex words (monosyllables like rump, plus one-and-a-half-syllable words like rumpus) containing the rhyme (or rime) /-əmp/
As can be seen from the chart in the link, mostly the -əmp words refer to 3-dimensional objects of about the same size in all dimensions (bump, stump, hump, rump, clump), but there are subsidiary categories, too. The word rumpus sits squarely in the middle of the Pejorative category, with a foot in both the Personal (chump frump grump) and the Aural (crump thump trumpet) subcategories.
I.e, rumpus is predisposed phonosemantically to refer to some unpleasant event that makes a noise -- and was possibly intended to make a noise, and possibly intended to be unpleasant, and therefore potentially involves human conflict. Phonosemantic "meaning" never commands, but it can suggest, and that's why it's all over the place in nonce words.
To me the words have very different connotations. Rumpus implies physical activity normally associated with playfulness whereas ruckus only has to do with volume and can be pleasant or, more commonly, unpleasant.