Bk-MDMA both chemically and in effects.
If youre wanting an MDMA experience, only MDMA is MDMA. It's best not to experiment with RC substitutes too much, the long term effects of many are unknown and potentially nasty. You are best off enjoying light psychedelic RCs like 2c-i if you are simply interested in fun RCs, but trying to achieve MDMA euphoria though RC experiments can prove lackluster and dangerous.