The Fujimi Graf Spee isn't a bad kit by any means. But I strongly recommend the Italeri one. The subtlety of the detail on such places as the after end of the superstructure is really impressive. And the way the hull is molded - with the underwater portion held on by narrow "gates" that get trimmed off - is downright ingenious. I built mine as a waterline model, but I could tell that the underwater hull piece fit perfectly. And take a look at the ship's boats.
The only significant problem with the Italeri kit is its representation of the "sail" mechanism. This was an apparatus for recovering the ship's seaplane. It consisted of a large piece of canvas rolled up to a boom-like gadget, which swung out over the port side. It was mounted on the boat deck. Italeri provides a part that only vaguely resembles the real thing. (Fujimi, if I remember right, ignored it completely.)
For a model of the Graf Spee at the Battle of the River Plate, this is irrelevant. The thing was so clumsy that the crew gave up on it and threw it overboard sometime shortly after the war started. I wanted my model to represent the ship as she appeared in 1938, during the Spanish Civil War. Cooking up a reasonable representation of the "sail boom" took about half an hour's work with plastic sheet and wire.
In that earlier period she was a particularly handsome ship. In addition to the heraldic devices beloved of the Nazis during that period (a huge gold eagle on the stern and the von Spee family crest on either side of the bow), she had red, white, and black stripes painted on her main battery turrets. I also found, in several photos, pretty clear hints that each of those turrets had its own coat of arms painted on each side. (I couldn't find any pictures that were clear enough to show what they looked like, though.) I've always found it ironic that two of the most despicable regimes of the twentieth century, Nazi Germany and the Soviet Union, produced some of the century's best looking warships.
The best book I found was a paperback called The Pocket Battleship Graf Spee, by Siegfried Breyer. It contains lots of pictures, most of them reproduced large enough to be a big help (and, incidentally, to confirm that Italeri's researchers did their homework - with the one exception of that "sail" gadget). I haven't seen the new Squadron book yet, but I imagine it's excellent.
Youth, talent, hard work, and enthusiasm are no match for old age and treachery.