I have attended a job fair last week. A few companies said that they are interested in my work and gave me their business card to contact them. I was wondering what will the best way to contact them and ask about the job or internship?
Unless they told you to use one specific method of contacting them, then either phone or email will work. Depending on the information on their card they could also ask you to contact them via social media or a contact method on their website.
One advantage of email is that they don't have to be near their phone and free to talk at the moment you call. Email also is easier for them to respond to you during non-standard hours. Of course email can get lost if it is viewed as spam.
I would lean towards email.