Now that Mailchimp cut their free plan to nothing, this is my default choice.
Fixes pretty much everything I hate about Mailchimp and its clones...there's no complicated UI, no bloated e-commerce style template builder, no silly landing page builder. Just a simple editor that works like a doc and clean templates.
A few kinks to work out since I think they're still in beta, but the team seems to be moving fast.
The way their forms work is best I've seen on any platform. It's just a simple POST url you can apply to any form on any website to make it function (even works on static sites).
Also, the Webflow integration is great, allows you to setup a Ghost-style newsletter with automatic cross-posting to your blog.