What might be better than looking for the "best" theme, is picking the theme that aligns with your goals as an organization and how you want to implement your LMS.
Generally there are a few key things you need/want when implementing a LMS. For instance, you might want all the features and tweaks you could ever imagine. Maybe you want simple, clean, and efficient. Maybe you need the LMS to sell courses or provide marketing. Each theme will have it's strengths and weaknesses.
The "Best" theme for you hasn't been defined in your post. Most themes are customizable. Most of the more popular ones are updated regularly and you can peek into the version history to see the frequency of updates.
Our goal in designing Fordson was to do a few things to speed up the process from login to engaged in learning. We don't automate enrollments like a college would. Each course used to use Self Enrollment, however, you still had to find the course and then enter an enrollment password or click the enroll button. We found this to be a chore with almost 2000 courses and users from age 5yrs to 18yrs, so we developed an enrollment plugin that functions just like Google Classroom codes and can even use QR Codes to enroll a student directly from the site homepage.
Fordson's site home is designed to help the student enroll, find a course, view their dashboard, engage with learning. We look at the site home as the "traffic cop" trying to direct the user. We have a large customizable icon navigation bar which can take the user to any number of locations such as Dashboard, calendars, etc. When using the Easy Enrollment plugin the homepage displays a large enrollment form where the student puts in the code and is instantly enrolled. There is also the ability to put text, marketing tiles, a slider, and other useful tools.
Once in a course we created a Course Management panel that displays all the needed links for a teacher to manage their course. All laid out and organized in a way that makes sense. As has been mentioned the version we are working on will have awesome new features that consolidates all the navigation into the top navbar. We even include a student course dashboard which displays relevant course information in a convenient panel. Our new version will also have a "location aware" editing button for teachers which will return the teacher to the exact same spot on the page when switching between edit and view modes.
We will be continuing to develop and implement community-driven suggestions and features as we move forward with the Boost-based theme in core of Moodle.
My best advice would be to define how you want the user to engage with the learning on your site and then look for a theme that best supports that. Providing too many blocks and other items sometimes introduced by the theme can just clutter up the page and make it harder for students to process where they are supposed to go and what they are supposed to do next. In my experience, sometimes less is more when trying to complete a very specific task such as what a student would need to do in a LMS. There are less "wrong turns" when the interface is clean, minimal, and direct.
