Which is better for poison ivy, claratin or benadryl (diphenhydramine)?

Either or neither: if all you want is to help relieve the itching one or two tablets of either one will help. But, poison ivy reactions are more than just itching and will require some kind of anti-inflammatory steroid. Over-the-counter hydrocortisone cream will help relieve the inflammation. Keep in mind that it will take up to a week for your body to get rid of any of those cells that have touched the poison ivy.

Either: Both will help control the itching. Neither will make it go away.