I switched from Gmail to Fastmail back in 2013 [1] and haven't looked back.
Fastmail has continued to make significant improvements, while keeping the interface lean and functional.
It seems to me like $3/month is worth it for a service as critical as email.
[1]: https://www.maxmasnick.com/2013/07/19/fastmail/ and discussion here: https://news.ycombinator.com/item?id=6069944