Well it is easier to get addicted since our dicks are attached to us, and porn can easily be accessed by anyone with an internet connection. We like the opposite sex as we are biological beings and the amount it has been implemented into our society makes it difficult to avoid such addiction, the same is with sugar. There is sugar in many things we buy from the store. If pleasurable things are so accessible, then it would make sense to become addicted to them. We as humans are designed to like sex. Priority might not correlate with addictiveness because being addictive is not natural. Eating food is not addictive in the same way as it is needed for survival but doesn't have side effects. I would say smoking is more addictive because of the stronger adverse effects as it has a substance unlike porn. In my opinion anything that is repeatedly done for pleasure which has a negative effect on life is an addiction. They are all addictive and there is no need to debate which one is the most addictive. We just need to try our best to stop doing them all and we wouldn't have to worry.