In general, I'd say Spanish might be the most beneficial. A large number of people speak it both natively and as a foreign language. It's also becoming more influencial in the States. In Canada, however, French would be a better choice.

I am a student.Assume that I have to travel much for my job.To communicate highest people which is the best language -help me pleasee:)

It all just depends on why you want to learn a language. Do you need Italian for your career? Do you love French literature and want to read it in the original language? Do you want to travel to South America?