The verdict
If you write, teach or sell digital products to an audience, I'd pick Kit. It is built for that, and the tag and segment model keeps working as the list grows.
If you run a SaaS product and people sign up, activate and cancel, pick Loops. Emails that react to those events beat a newsletter tool with manual tags.
A software company with a content audience on top can use both, but I would not at first. Pick the one that matches where most of your contacts come from. If you need deal pipelines or lead scoring for sales, neither is the right base.