It's up to you which pronunciation you favour. Yes, in most parts of Spain (but not all) 'c' before 'i' and 'e' and also the letter 'z' are pronounced with the same 'th' sound that we use in English. This is known as speaking with 'distinction', as there is a distinction between the pronunciation of 'c/z' and 's'.
In Latin America they speak with what is known as seseo, where 'c' before 'i' and 'e' and 'z' are pronounced the same way as the letter 's.' This also happens in several parts of Andalucía and the Canary Islands. The majority of the Spanish-speaking world uses this pronunciation. But as I initially said it's up to you which you favour and it's going to be dictated by the type of Spanish you learn and who you come into contact with.
Myself, I learned Spanish from Spain and 95% of my contact with native speakers has been with Spaniards so I use distinction when I speak. Another thing to consider is that the 'th' sound does not exist in many languages (French, German, Portuguese are just some that come to mind) so many learners tend towards using seseo. I believe there is a 'th' sound in Arabic so this won't be a problem for you. This is also not a problem for native English speakers but most Americans who learn Spanish would use 'seseo' because that is how they talk in the Spanish-speaking countries closest to the US.