My son swims. Backstroke is his least favorite though I think he hates everything but free
Backstroke is only uncomfortable in terms of seeing where you're going. Otherwise it's quite relaxing.
Breast stroke is the easiest to learn, as you can breathe every stroke.
Freestyle (front crawl) demands that you learn to breathe on alternate strokes, but is the fastest.
Butterfly is just fucking awkward. It's like Olympic walking, it's a particular style enforced for that event but isn't the best way of getting anywhere in real life.