What is the difference between creed and credo? They seem to have the same definition in online dictionaries. Do they have different connotations?
They are interchangeable, but I think there are some subtleties that may or may not be important.
A creed is often a shared and established statement of belief. The Nicene Creed was established to be a statement of faith symbolizing a shared understanding of Christianity between believers.
Credo, or "I believe," tends to be a personal statement and is not necessarily bound by a group. My personal credo could be, "Bacon, always."
Credo could be seen as more formal, since it's from the original Latin, but I'm not aware of any other specific connotations for either word.
Creed is an English word, and credo is the Latin word it is borrowed from. Creed would probably be the preferred term unless you wanted to use a non-English word for some reason.
To me credo has a connotation of a personal belief. Almost a tagline. I think these are sometimes used light heartedly. jboneca's 'Always Bacon' is a fantastic example.
A creed to me implies a more formal statement of belief (church) or ethics (business). It carries more conviction. ex Assassins Creed , Nicene Creed, etc.
This is my opinion and reflects how I have experienced their uses. Research clearly supports jboneca's statement that creed is based on credo.