It is easier to cut the part when it is flat. However, if your bends will be very close to your cut out, you may get unacceptable distortion due to the inability to adequately clamp the part. If you think that might be the case, it is easier to bend first and then hassle with cutting a more difficult to hold part. Do you know what alloy/temper you have? Trial bend a scrap first. Some alloys do not like to be bent very far before they crack.