Seeing both models. There is no right or wrong in my opinion. My belief in it's more down the individual leading the function i.e. If the marketing leader is very sales focused, understands sales process and demand gen (in a B2B context) then well placed to manage SDR's. It helps connect the two functions. If the sales leader is not purely focused on AE's and has a great connection with the CMO. In this scenario it could work to be under the sales leader. The key principle is the focus being on integration between the two functions. If there is good integration the structure will work.
If not, regardless of reporting line - it will fail.