Which type of firm is best for summer internship?

It will depend where your interest lies is it sales, is it marketing, if sales or marketing then what would you prefer product or service. But if i need to point out a single sector, then banking would always preferable

Being a marketing student, you should know how to sell a product in a market. Go for a firm or sector in which you have interest. Try for top 25 marketing companies like Nestle, Pepsico, samsung , ITC, Cadbury to name a few.