hmm...i guess his deal was to play a part in capturing han solo & co for the purpose of baiting some guy named skywalker, after which they'd be freed . vader, in all his evilness & treachery, twisted the deal to involve the permanent detention of leia & chewie and the handing over of han to fett.
as to whether he made the right choice, i am of the opinion that, yes, he indeed made the more practical & correct choice for the reasons u all have stated.
If that's the case, I don't see how Lando betrayed any of them.
he betrayed them by giving them to vader in the first place. regardless of whether he intended them to be freed later, by handing them over to vader alone, he committed an act of betrayal. i think that han, leia & chewie, in all their humanity (as in, everybody's human) came down a little hard on lando for his act of betrayal, given his lack of choice.