What should I consider when choosing between these phrases:
suffice to say
it suffices to say
suffice it to say
I don't know about the second and third one but I can speculate that the first one ("suffice to say") is not obsolete, at least in the USA. For instance, in an episode of the TV series, Dexter, there is a conversation that goes like this:
[Dexter]: Deb found out what I am. She knows everything.
[Dr. Vogel]: Everything? How?
[Dexter]: It's a long story. Just suffice to say she's not handling it well.
So, I assume in similar situations it would be safe to use the phrase "suffice to say", yet I don't know when I'd need to switch to another alternative (after all, I don't like to mess with the Mr. Potato Head!).
Best Answer
All of the forms are valid, and in common usage in English.
"It suffices to say" and "suffice it to say" are the same, just with a word-order inversion for stylistic purposes. "Suffice it to say" is more old-fashioned, but it seems to be coming back into fashion (since about the mid 1950s), and is now more common than the word ordering "it suffices to say" in both American and British English.
"Suffice to say" is also valid; in this case the "it" has merely been elided, and in my experience is more common in speech, whereas "suffice it to say" is more common in writing.
The following is an NGram that shows that all of the forms are relatively common, and you will be widely understood by native English speakers whichever form you happen to choose.