I agree with what another said, there are going to be pros and cons with both. However, I like PBS but it is the only thing I know besides the crappy USAF stuff.
I'm in a unique position. I am in a junior base on the junior equipment and I'm in the 50% percentile. Typically, there are only 4-5 lines underneath me before the reserves lines start.
Even though my seniority isn't very high, I routinely get lines I am happy with. In fact, I tend to take the stuff that others don't want. And everyone seems to want different things, so it has a way of working itself out.
Now, when it comes to the big holidays that everyone wants, of course, seniority is going to come into play. However, even then, people at the bottom of the list can get lucky.
My company used to have hard reserve lines built. To me, that was aweful. If I needed some days off (for example a birthday here, a party there ..etc.), it was impossible. With PBS, I can put that in my preferences and PBS will do everything it can to build me a line around that. And now that we PBS reserve lines, I can get just about any sequence of or any days off that I want .. provided im not asking off major holidays or all weekends.