In Saudi Arabia Which language is more preferable english or arabic?

Definitely, it is Arabic. English is spoken by people who were sent abroad for scholarships. Each of them reflects the accent of the country he was sent to. There are numerous international schools specifically in major cities like Riyadh, Dammam and Jeddah. Some private schools teach English from K to12. There are many native speakers and ESL speakers of English who work in the K.S.A. Therefore, it is easy to say that English has a massive popularity in the K.S.A. 

Arabic most preferable.

Then English, spoken in an American accent (especially by the young generation).