The argument can get quite heated, depending on who you talk to. Some people are adamant that you should make the most of the space provided, that it’s a wasted opportunity not to use the back of the card for more information and the chance to promote yourself and your business.
On the other hand, there is the argument that you shouldn’t just treat your card as a billboard and exploit every square centimetre. Leaving the back of the card clear gives you the chance to put something really relevant there that will make it memorable to the person you’re handing it over to. Most people hand out cards after speaking to someone at a networking event or meeting of some sort, and getting a pen out to make a note of the next arranged meeting, or a suitable reminder of the conversation (e.g. “daughter needs business cards for her new shop”), all helps to really make the card memorable.
Personally, I prefer single sided so I can make notes on the back, but this has much to do with my advancing years and declining memory. It really is a case of whatever suites you personally, because despite what the blowhards on either side of the argument might tell you – you’re absolutely right!