Digital marketing seems to cover a bigger market than social media marketing which is social media centric. Digital marketing might offer you better job opportunities with a good pay
Do digital marketing is better. I have also done it, it opens more opportunities. And more internship also. Social media marketing and SEO and other all come under this only. You will get a brief idea about everything.
Digital marketing is a better option as social media marketing is a branch of digital marketing itself, while learning about digital marketing you get to learn about social media marketing, blogging ,seo and many other things.