The only major differences, -50% exp and you cant or pkon at anytime. You can still duel and arena fight. And it is the most noob friendly server at the moment. If you join any other server you won't be able to dp without a high level pet since most dp's won't invite you unless you have one, and SS will be impossible to buy in Rappelz until higher level when you start making more rupee's.
Unicorn which is great server. As you will always find a dp in your range, and Unicorn just way more rewarding to play. And it doesnt take as long as you think to level(Rappelz Gold). The essential part of the PvP system is still intact (rappelz rupees), and its not way overpriced like the other servers.
At last it is better go to Unicorn if you will get very upset if you get PK'd. It is where will it be easier to get a DP and learn better your class and pet skills-so please choose Unicorn. Our Rappelz powerleveling service will make your level up quickly.