I did Keto when it was called Atkins. Had good success with it, but not life changing
I prefer IF, because it lets me adhere to a pretty severe low calorie count. Just have some caffeine in the morning, and by the time I finish my workout I'm ready for my first meal. From there I just count calories and keep it low, which is easy to to because there's only half a day left.
Coffee is fine during a fast