Sorry, I'm not sure there's an easy answer... Depends on what they're going to do with them.
If I was preparing them for someone in my epidemiology department, I'd probably send them the excel workbook with text boxes describing the key messages of the graphs, as I'd expect them to tweak the graphs as they like.
If sending to someone with less analysis skills, I'd send it in a word document as a report if I needed to describe assumptions or limitations with the data.
If they wanted graphs for a presentation, I'd probably put them in PowerPoint with a key message or two for each graph.