We are supporters of Swim Smooth; it fits most of our needs by helping to decide what type of swimmer you are.
I steal the best bits from many systems. I spent 5 years teaching children from 3 – 10 year olds to swim, 15 years coaching clubs and individuals in the UK, Germany & Switzerland. This has given me an experienced eye.
For athletes who are not local I get them to do a short film of themselves swimming using an iPhone or similar. Normally we can see enough measure what you are doing and to make improvements by using the appropriate sessions and drills.
For athletes who are local, I come and watch you swim and if possible take a short video.