If you are only going to buy one pass, it can be a hard choice.
At Brighton you will have a good selection of rails, but a lacking jump line. However, when you want to leave the park, there is a lot of very fun terrain at your fingertips, especially if you include the backcountry/slackcountry access.
At PC, you will have a amazing park filled with a million newschool skiers. You will certainly love that part. But when you want to leave the park, the rest of the mountain will leave you wanting more. Sure you can find some fun stuff, but there isn't that much there, and it will get skied out really fast.
It's really up to you. It depends on what kind of skiing you are looking to do. If you only want to ski a few pow days a year, you could get a PC pass and either search PC on a pow day, or buy a couple day passes to a Cottonwood resort when a big storm comes in. If you want to ski a much more even amount of park/pow, get a Brighton pass and just hang out there all season no matter what you want to ski,