Really? You wanna know if it's better to be bisexual or not, in order to "be poly?" Well, what orientation are you? I would say it is always best to be yourself. You seem to be putting the cart before the horse.
Living polyamorously and having multiple relationships is no different, in many ways, than having one relationship and being monogamous. The same key elements need to be in place for any relationship to work: mutual respect, caring, honesty, clear communication, affection, etc.