Not only is a business card a highly professional item that will make your company look trustworthy and successful (particularly if you go for plastic cards printing or matte laminate cards printing), but it's also something that can contain a lot more information than someone can remember in one go. This means you can put down a phone number, an e-mail address, a business address and a website which they can then use to get as much information about your company as they want.
Compare this to simply telling someone where you might meet them in a bar or at a social event over drinks. Here there's noise and commotion and there are lots of distractions. We know hard it is to remember the name of a person, let alone the name of a company, and that's exacerbated largely by drink. At the same time it's not just the name they'll be forgetting, but they'll likely forget they spoke to you at all and that there was even anything they were meant to be remembering.