ResidualVM has been incorporated into ScummVM, so out of the two, it's ScummVM that is more likely to work properly. ResidualVM is the one that's been left behind so it won't benefit from whatever recent bug fixing has gone on, if any!
I've been playing EMI through ScummVM and it's kinda okay, but buggy for sure. Minor stuff like shadows looking bad and some dialogue lines being cut off, but also weird stuff like characters wandering around the wrong screen and one place where you can make the game crash consistently if you do a particular thing. And I'm only on Lucre Island, so there could be worse to come! Sounds like I should investigate some of the options in this thread.