Many will agree that more than 50% of internet users are on mobile. However this may not translate to repeat customers in the case of online businesses. Many online businesses devote most of their energy towards capturing these users.
My advice is to focus more on the desktop/laptops users because most times, these are the people who are more relaxed either in their offices or homes and are ready to buy your product. Also the bigger screen gives them more information that may ultimately influence their buying decision positivity.
Most people using mobile are either on transit or not in a condition that will warrant them to buy your product. Also the small screen in mobile phones is not convinient when you have you have type in you debit card details or fill a form to make purchase.