Can only comment on the first two. Coursera: most courses come from universities.They are structured,aims are clear. Depending on the level and the teacher,some

Can only comment on the first two. Coursera: most courses come from universities.They are structured,aims are clear. Depending on the level and the teacher,some can be dull or/and going 1000 miles an hour,so picking the right level is important. Udemy: less formal,less academic. Some courses are created by those who have no idea what they're talking about,while others are well prepared, broad,and deliver high value.