Premier is supposed to be the higher end line for Pioneer.
My experience from them is mostly from many years back. The premier line had better and more features then they're regular pioneer counterparts (pre-out volts, eq options, etc). From my experience the features vs. the price difference made it worth it, but I had a good shop that gave me premier stuff at prices barely much more then they sold the pioneer stuff for.
I have about an 8 year old reciever that is still going strong. Also I have 2 of the aluminum looking subs (ts1040 ?) that hit hard and very clean. I just refuse to give them up. The premier amps that came out about the same time also sounded very good and were underrated. Their aluminum line components from them were nice to but to harsh on the highs for my tastes, I preferred the reqular pioneer comps over them.
How premier is nowadays, I have no clue in the car audio world. From specs and features I've glanced at, they've lost their edge. In the home audio world mostly premier is better then regular pioneer, but a few pioneer units top premier units.