Quote Originally Posted by John_Douglas View Post
I'd say there's very little difference when you're speaking in the first person saying "I need to" "I have to" or "I must."

There are also differences in usage, with "must" being much more formal.
I definitely agree that "must" often sounds strangely over-formal in colloquial speech.

Regarding "need to," it can sometimes emphasize "physical necessity" more strongly than "have to". So if you say "I have to go to the bathroom," it's like "I want to find a toilet in the next 30 minutes or so," but "I need to go to the bathroom" can mean "If I don't find a toilet in the next 5 minutes, there's going to be a huge mess in my pants or on the floor!!!!"

But otherwise I'd agree that "must," "need to," and "have to" are quite similar.

They all have very subtle differences between them and it's impossible to give an exact correspondence with English verbs like need, have to, must, should, ought to.
For Russians, I would recommend using modifiers such as "perhaps," "possibly," "probably," "definitely," "really," and so forth in order to make your meaning more clear, instead of trying to distinguish subtle shades of meaning with the English verbs alone. (Even though a native English speaker might be able to distinguish the meaning without a modifier -- such as by slightly changing the pitch/intonation of the sentence to make the verb more or less emphatic.)

P.S. Or, you can use entirely different verb constructions -- "I've got no choice but to (do something)" or "I feel an obligation to (do something)" or "It would be the right thing for me to (do something)." Here, the difference in meaning is much more obvious than with "must", "have to", "ought to," etc.