From what the people at the Apple store told me, you don't need one. Apple rarely has malware - Microsoft seems to be the whipping boy for malware - and Apple is good about adding any antivirus to your updates. This goes for the ipad and iphone only. The Mac's do need antivirus software. So as long as you do the updates, you should be good. I've had my iPad for 5 years and have never had any problems. At least that's what I was told at Apple. My best advice is to stop at an Apple store and ask them.
I do suggest that you download the Adblocker app though. Makes a WORLD of difference when on the web!