I've been paying for mailspring for a few years now, and I love it. It has touch and gesture support, is open source, and is available on Windows, MacOS, and Linux.
Its paid plan includes some nice features like email tracking - which you can't really get from just a simple client and (needs a server to track who has opened an email and when) - and id lookup, for things like quickly seeing the LinkedIn profile of a sender not in your contacts list.
Definitely my favorite desktop client by a wide margin, and one I would recommend wholeheartedly.
Edit: Just to be clear, it's available for free as well.
Local only.
Even if you pay for their subscription, when you get to a new computer you need to manually authenticate with each service. But, it remembers which accounts you have, so it's faster than manually setting up each account from scratch. Basically "we know you have Gmail, xmail, ymail - tap each account to reauthenticate"
It's a good way to have (part of) the convenience of a cloud service, while combining it with the security of local only clients.
Edit: all of this is optional, you can choose not to let their cloud service know of any of your accounts.