What is the difference between them ?
Beside Premier cost a grip more

 

Premier = better warranty, usually more options on the deck and higher voltage pre-outs.

 

but look-wise and sound wise, is the premier better than base ?

 

Yes the premier will be better sound wise if you are using amps. Also on some of the models the eq has a pro mode, which allows for better tuning of the sound. Go and look at http://www.pioneerelectronics.com and they have a compare decks features and select one deck that is a regular pioneer and one that is a premier. ie. DEH-p8600 and a DEH-P860.