On one hand, these are all valid GOO familiars.
My favorite so far is the warlock's own shadow. When she sends it to scout ahead (a common use of familiars), and the other PCs watch the shadow detach itself and slide across the floor... that's gonna be an awesome moment. See also, the Judy Garland and Frank Sinatra versions of "Me And My Shadow".
"Check, please! - No, I mean a SANITY check!"
On another hand, Lovecraft's writings include many GOOs (and outer gods and elder gods) who are neither Cthulthu nor Azathoth. If Randolph Carter were a Warlock, then the most appropriate form for his familiar, would be a cat from Ulthar. (With more abilities than a standard housecat. Ultharian cats kick ass. They'd kick ass and take names, but they don't have the attention span for that.)
A sea-pirate warlock with Nodens as patron might have a familiar in dolphin form:
"And upon dolphins' backs was balanced a vast crenelate shell wherein rode the grey and awful form of primal Nodens, Lord of the Great Abyss…"
Night-gaunts serve Nodens as well, and night-gaunts are more in the middle of the Stereotype Zone.
I'm just saying, the middle of the Stereotype Zone is sometimes the most fun, but not always the most fun.