The debate can go on for days. For me, it comes down to pow days. Two years ago, I got a pass at Bridger. It was an amazing snow year and we were skiing pow all the time. However, towards the end of the year when it stopped snowing as much we were skiing short, mogul-filled runs. This was enough of a reason for me to get a pass at Big Sky the following year. I was glad with my decision because the snow year wasn't as good and on the days with less snow we could still mob the groomers, park etc, whereas I would've been skiing short mogul filled runs at Bridger. Big Sky definitely doesn't get skied out very fast, just on the popular runs. We've been there a week after a pow day and got good turns. I'm getting a Big Sky pass next year.
Also, depending on how old you are price might be an issue. 18 and under gets a Bridger pass for about $375 I believe, but older than that and you're taling 700 dollars, which is only about $100 less than a Big Sky pass....