Choke and suffocate can be both transitive and intransitive.
"I choked" "He choked me"
"He suffocated" "You're gonna suffocate him"
"Suffocate" sounds stronger and more formal -- it gives the impression of death.
Smother, strangle, and stifle are all just transitive. "Smother" focuses
on someone placing an object over someone else's mouth and nose so that
they cannot breathe. "Strangle" is more like putting something around
someone else's neck so that they cannot breathe. "Stifle" is more used
in idiomatic expressions -- "He stifled a laugh," etc.