Very similar features. Remember the Milk has been around for longer and has constantly been improving by adding features such as integration with Zapier and IFTT; enabling attachments from Dropbox and Google Drive; integrating with Google Assistant and Siri; and smartwatches. …
If you want a customizable solution that can be adapted for just about any scenario, I recommend using Notion. If you need a solution that's easy to share with people outside your organization, Notion is great and allows individual or team permission-setting. If you want a turnkey solution, Notion might not be the best since it requires a fair bit of set-up. There are templates that can be purchased to handle this, but I haven't found them very helpful.
I think Remember the Milk is a great tool for managing tasks and information. However, it depends on what the person is looking for. If you are looking for just a simple task management tool without any bells and whistles, this may be a lot, as it has a lot of advanced features (and even more if you go pro). If you are looking for a more robust task management tool with the option to add priorities, tags, categories, and assign tasks to others, this may be more suited for this. It is also helpful for managing lists like shopping lists or project lists.
I use Notion on my personal tablet, and unlike on the computer, I have a lot of difficulty editing backgrounds, GIFs, and page dividers. It's not as user-friendly, and often the elements end up cut off or misaligned, which is frustrating.
While the current calendar feature is helpful, I'd love to see more customization options. The Google Calendar style isn't always ideal, especially for tasks without specific times or for ongoing projects that require daily maintenance.
It would be fantastic to have more flexibility in customizing Notion pages. For example, I'd love to create planners with the freedom to add illustration boxes, stickers, or GIFs without being restricted to a fixed layout.
Very easy to use (I learned how to use everything on my own) and I was able to set up an entire ecosystem without any courses or other tools. I often say that Notion is like Lego for adults, because there we can use all the available tools to create a multitude of things, from funnels to projects with calculated deadlines and tags.
The company uses both Notion and Trello within the company. Notion is more for North America employees while Trello is used between Operation team overseas and in North America. Sometimes it's a preference of how the tools look like for project management. I would say both Notion and Trello are nice tools and serves our needs.
Google Tasks is a much simpler task-keeping interface, and I use it for the most important tasks on my phone. It does not offer tags, priorities, or distinguish between lists/tasks. It does let me star tasks, but does not let me determine the priority levels. I can also move tasks to different lists, but they can be hard to manage if there are too many, so I generally do not use this feature. For me, Google Tasks is ideal for very simple "I need to write this down" type tasks that are of high priority. It is not a good brain dumping tool because tasks can easily get lost. This is more for those nagging tasks that I want to do and make sure there is an appropriate alarm for. It also integrates well with my Android home screen. However, when I have lots of tasks I want to categorize, or I do want to do more of a brain dump type thing, I think Remember the Milk is far better. I can have more control over priorities, tags, assigning tasks to others, and other robust features.