Guaranteed that you will get big mountain with either option. Big Sky has a bit more "AK" style skiing if you will. The good shit is above treeline. Big fast lines. Most cliffs up to must be sent with a speed.
Bridger on the other hand is a bit different. The skiing is a bit more techy (per square acre) and there are some playful sick lines to be had.
The major downside is the crowds. If the snow is good, expect 45 minute lift lines.