I've been playing Fallout New Vegas since 6am the day it was released but because I want to take my time, experiencing every location, picking up every 'small book', 'empty bottle', etc. that I find, and switching off between 4 different types of characters that I'm playing through simultaneously, I've not gotten through more that a quarter of the main quest yet. My question is this, When all is said and done how many totally different paths can you take to finish the game (by this I mean: at a certain point in the game, you're going to make the decision about who you're going to ally yourself with and not interact with any other factions, other than killing them, and be able to 'complete' the game). Based on what I've read it seems that your ultimate options are: NCR, Caesar's Legion, Mr. House, and Your Self (via Yes Man). Am I right? Can you ally yourself with one of these four groups, turn your back on or actively destroy the other three, and 'complete' the game? And furthermore, just out of curiosity, what did you choose?

Yes you are right but, with yes man you can not kill him or anything like that.
And I choose, NCR then Mr. House then Yes Man and now CL.