I never considered a Gmail alternative since Gmail has primary/social/promotion/updates tabs and proper threading of replies and almost perfect spam protection. What services do the above things as good?
I will say, however, that I never realized just how infrequently I receive mail that actually warrants my attention (let alone a reply) and that feels sort of lonely in a funny way.
• Does not ask for phone number.
• Allows actual aliases (instead of a self-defeating YourRealAddress+Alias@Gmail.com)
• Does not sneakily sign you into Search and every other Google service when you just want to check your email.
In addition to all the privacy advantages.