My bonus has always been in the 10% of my salary range until last year.
Last year we got a boot in the ass and the asshole closed the shop for three weeks. A bonus would have been rather silly after losing $4000.00 in income for the three weeks out.
Cash for anything is always better than a gift card. Gift cards will sometimes charge you 5 bucks to activate and some have an end date that you have to pay attention to.
If you're giving out over 600 bucks, your employee has to pay taxes.
They only take taxes if it's a check, States vary but the federal rule is cash gifts under $12,500 don't have to be reported..
I would go with cash, GC's are good, but with the economy the way it is cash can be put toward the house payment/rent, or other needs .