All data has been taken from @DdmrDdmr Merit Dashboard where you can find bunch of interesting stuff, if you wanna go more in depth.
Number of posts ( May 2020)
It's not a surprise that two most active boards are Marketplace with all those active child boards and Marketplace (Altcoin) due bounty campaigns. One would think that Bitcoin part would be more active, but I guess in most of those child boards write people that have more technical knowledge or interest in Bitcoin.
Number of merit (May 2020)
Since marketplace is by far the most active board, it is not a surprise to see it at the top of merit shared, followed closely by Economics. As expected, altcoin boards are at the bottom of the list, and it is a known fact that it is probably harder to get merit there than any other board.
Merit senders/receivers (May 2020)
Those numbers usually follows the number of merit shared, with a few exceptions like Beginners & Help that has high number of senders/receivers compared to merit sent. That is a good thing I think, as lower rank members are usually active there.
Merit/Post ratio (May 2020)
Altcoins boards are once again at the bottom, not a surprise there, same as more more technical and serious boards being at the top, with Meta of course.
