Although the London Review of Books is my favorite answer to this question, the New Yorker is a close second ... I find it very readable on a kindle. They are

Although the London Review of Books is my favorite answer to this question, the New Yorker is a close second ... I find it very readable on a kindle. They are doing great journalism and I've been very impressed with their long form writing on topics such as the aftermath of the BP oil spill, the Ferguson shooting, etc. I subscribe to the kindle version of the New Yorker (which includes the comics) and the print version of the LRB (which is a large format magazine).