Gift cards are better than gift vouchers because they are shiny.
This is obvious to me, so obvious in fact, that I was initially reluctant to give any other argument on the matter but I feel it my duty to give a few more points.
With a gift card you do not have to try to spend the exact amount on the card because any left over will remain there. In the old days of gift vouchers most places would not give change from a gift voucher so you would end up losing the difference or having to buy something more than the cost of your voucher.
A paper gift voucher gets tatty if kept in a purse or wallet too long. A gift card stays in good condition.
Gift cards are nicely decorated with pictures and patterns whereas vouchers were only embellished by anti-fraud measures.
The only negative point about a gift card is that if it remains unused for a number of years it becomes unusable and the money reverts to the store but the same was true of an awful lot of voucher which were printed with expiry dates.
And did I mention that gift cards are shiny 🙂