silly fat cats (or) fat silly cats
Silly fat cats is more euphonious. Both are grammatically correct.
'Fat cats' idiomatically means rich people, or rich powerful people. So it could be that you are calling those rich people silly, as opposed to calling those silly cats plump.
funny fat cats (or) fat funny cats
The rhythm of these phrases is about the same, so either.
funny big fat cats (or) big fat funny cats
Big fat funny cats rolls off the tongue. It has much better cadence. So definitely big fat funny cats.
funny really big fat cats, or really big fat funny cats
Again, the cadence is the deciding factor - really big fat funny cats.
really in this situation means "very", and modifies the adjective which immediately follows, so you are right to move the adjective "big" along with it...
Compare
A really expensive black leather handbag/purse.
This bag is black, as well as being very expensive.
An expensive really black leather handbag/purse.
This bag is expensive, as well as being very black.
I have seen three films in the last week. I didn't like the first. I liked the second, but I liked the third best.
You can say I have seen three films in the last week. I liked the third best or most.
But in you statement, you are comparing two films. You say: I didn't like the first. I liked the second, but I liked the third best. So, I think, you should say: I liked the third much better or I liked the third better than the second.
Best Answer
It sounds fine to me. You aren't the only one to doubt the word, though. See: Twitter Users Call Out President Obama Because “Madder” Isn’t a Word, Except That it Is.
This might be a relative cultural thing, based on where you grow up. An example of what I mean is people pronouncing ask as if it were aks (or, what I hear, axe). It sounds totally ignorant to my ears, but apparently in parts of the American Northeast the usage is quite common even among well-educated people.