Hi Saioa
My personal favourite is C beacuse it gives you an ease over programming. Morover C is an user friendly language, unlike assembly which require lots of instruction sets to be remembered. Further, when you write a code in C, it anyway gets converted into its assembly level because it is easy for a computer to understand such language. C gives you a more systematic approach to write a code and understant it in a better way. Lastly, it all depends upon you. I would suggest to try out both of these languages a chose any one of them accordingly.
Good Luck 