Preferred anchor type for a Soffit connection

Thanks for the question, it would be a fastener that is suitable for the tensile zone i.e. cracked concrete and then it would come down to load(s) , spacing, edge(s) slab thickness, fire , corrosion conditions etc Screw anchors and expansion anchors both have their merits as indeed chemical anchors as another option. I'd suggest running the requirements through the Profis Engineering software as that will point you towards initial workable solutions which you can then fine tune.