Mehere@Mehere for LAMY, I prefer fine nibs because they work perfectly well with my Noodler's Black. For my pretty LAMY turquoise ink, I use a Muji Fountain Pen which is kinda between Fine and Medium. I suggest Fine.
MehereDepends on what your writing style is. I like to write small, precisely, and put less ink down so I almost exclusively buy Fine or Extra Fine pens. If you write larger go Medium or Broad. With this pen if you get a nib that's the wrong size for you then you can buy a different nib and change it out. Sounds like this might be your first fountain so I'd go Fine or Medium to start out with and go from there. The other consideration as you get different pens is that European pens tend to have broader nibs than Japanese pens. So, a Fine in this Lamy Safari is closer to a Medium nib on a Pilot pen.