I would also recommend you use both options, depending on the situation. Sometimes, when you have fresh information you would like to add, it's a good idea to update an old post instead of writing a new article, which is very similar to the old one. By updating an old post, you will avoid repetition of information and targeted keywords. As, search engines are considered to love longer and highly useful posts, you can simply update some old posts, and you can indicate the date when the article was updated. And, if you want to target new keywords, then writing a new post is the better option. Also, you need to be up-to-date with the trends, so write about what people are looking for the most, but write it in a more useful and unique way than the other people do.