I know Brian Head is closer, but I'll have enough time so that the extra couple hours of driving (each way) won't be a deal breaker. Never been to either place and Brian Head sounds nice, but Mammoth has so many more (and longer) runs that it's tempting. Of course I'll be watching the snow reports over the next week and a half, and if one place has significantly better snow conditions than the other that'll probably make my decision for me.
But just looking for opinions: if snow conditions are roughly similar at that time, and you didn't care about the extra drive-time or higher ticket prices at Mammoth, would you go to Mammoth? I'm an intermediate comfortable on any blue run and milder blacks.
Speaking of ticket prices, would anybody be willing to mail me a Terrible Herbst discount coupon for Brian Head? :-) I'll have a rental car, but won't need to gas it up before driving to the ski resort (and I think you have to fill up to get a coupon at Terrible Herbst?)