Do you say "I am torn between A and B"?

You can say this. 
It makes total sense.

That's a common way to say it.

Yes.
     That's  a good American English way to say that.

So says Natalie Imbruglia.  

https://www.youtube.com/watch?v=VV1XWJN3nJo

Yes, it's perfectly natural and correct.

Although I'm not a native English speaker, I would use the word: Undecided (I'm undecided between A and B), or: hesitate ( I hesitate between A and B ).

♥ @Anonymous: I love this song by Natalie Imbruglia! 

Yes, that is good idiomatic English.