MHX or Jack

I dunno if someone already post this but trying to differentiate this two 5* assassins.... which of the two has the edge on the crit team? What is the advantage of X over Jack and vice-versa?.... Any facts , suggestions or criticisms are welcome :)))

(I didnt have a support Jack (have Okita, MHX and loads of Scath-sensei supports) so I have no experience using her, but i battle her last saber wars makes me use 1 quartz for full revival of my servants...)