flap disc for surface rust removal?

Hey guys,

I was wondering if it's OK to use a flap disc and an angle grinder to remove the surface rust I have on the body of my 73 sport? Or is it better to use a DA sander with 60 grit? I know the flap disc takes off material a lot faster, but it may do damage or very uneven sanding. What have you guys used? Here is a pic of the body in question.