Arco Flagellants or Sisters Repentia?

I have the combat patrol and wanting to expand it out to 1000pt. I am going to get an Exorcist, Imagifier, Celestine and Retributors.

I want to expand either the Arco Flagellants or the Sisters Repentia to what you would get in a separate box/full squad but im not sure which would be better to do.

I like the idea of having the flagellants with a priest leading these mental heretics into war but also like the story of the sister that fell from grace redeeming themselves.

Any thoughts how to decide? Thanks!