Nothing wrong with Postman at all, but I just like Insomnia's cleaner and less cluttered UI. However, even as a regular user, sometimes I find the 'Send' button can be a lot more prominent than it is. The green '200 OK' response next to the Send button looks more like a button, and I keep inadvertently clicking on it to send my requests off!
And when starting out with a fresh workspace, the 'Create New' prompt looks like a button that you can click to create a new query, but it isn't - you still have to use the hotkey to do so. Small improvements in the UI like that will go a long way to making this my default 'go to' API testing tool.