I have used Intervals.icu before, but only to a very small extent. The manner in which the data is presented was cluttered and "busy". I found it hard to focus on the info that was most important to me. I'm sure there are formatting options that would have fixed this issue, but at the time I was not interested in figuring out to how to change the presentation into something more focused and easy to read.

Per your recommendation I went back to Intervals.icu for another look, but came away with the same conclusion. As a result, I decided to give TrainerDay a go. The interface looked easy, intuitive, and uncluttered. I also really like the custom workout creator! It's super easy to use. For only $3.99 per month for the premium version it seemed like good value for money.