In litigation, the court can compel the release of documents and information that may not be obtained through mediation. Parties in mediation may feel they don't have all of the necessary facts to settle. Because mediation is non-binding and voluntary, either side can decide not to continue with the process. Arbitration, on the other hand, tends to feel more like litigation as it follows a similar process. Arbitration is mandated for many disputes by statute.
Arbitration is generally faster than litigation, and depending on the case, can be cheaper.
Arbitration is binding, but the parties get to choose the arbitrator. Also, courts don't generally overturn an arbitration award. However, arbitration has limited discovery and the rules of discovery are relaxed, so one side or the other may still not be able to get all of the information it needs. Generally, there's no appeal, and this is a known risk of arbitration. Arbitration can be costly if you add up the arbitrator's fee and the fee for the administration of the arbitration, particularly if the arbitration is lengthy.