When resubmitting a paper, should I write individual letters for each reviewer or one common letter? My question is simple. When resubmitting a paper after review was done, should I include different response letters to each reviewer, or should I include my comments addressing each reviewer remark in a single letter?

Edit: I usually send one single letter. However, recently, I was in a situation where the reviewers made only minor comments while the editor had a major issue. I'd think the editor would not necessarily want to share his major comments with the reviewers, so I sent separate letters so the editor might choose which ones to send to the reviewers. This made me think that always sending separate letters is possibly the best practice.

Edit 2: Please note that I'm not asking how to write good response letters in general. I'm sure there are plenty of good advice about that on Academia.SE. I'm particularly interested in pros and cons of using single vs multiple letters.
Usually, you sent back one single letter in which you answer the reviewers questions one by one. I always start with a short note to the editor, listing the major revisions done as bullet points. I also thank the reviewers for their time spent on the review and that their comments advanced my manuscript (of course I write this only if the review really improved my work). Then I start with "Reviewer 1" and list each of his questions or remarks and mark my comments either in bold or in a different color.