Who has the claim to them: Belgians, Swedes, and Greeks. Who gets them? That depends on the game.

Firstly, Germany can assure himself Belgium if he a.) moves his Kiel fleet to Holland; b.) moves his Munich army to Ruhr and; c.) is cooperative with either England or France. If cooperative with France, Germany won't have to worry about a move to Burgundy and if cooperative with England, Germany wouldn't have to worry about Denmark. This also ensures that Russia can get Sweden, which can be a huge misstep if a juggernaut arises. If England and France align, they can support one another into Belgium and block Germany. Any combination of those three nations in western Europe can easily take out the other, though Germany (in my opinion) has the advantage in gunboats, especially if France doesn't open to Burgundy. Germany can also be "robbed" of Belgium by Italian aggression against Austria which would threaten Munich. Russia and Austria can force Germany to defend rather than get three builds as well, but that's rarely seen in full press. Obviously, German movement to aggressively take Belgium is risky.

Sweden is an important territory to Germany, England, and Russia. My preferred opening as England is to work against Russia to get Scandinavia, hopefully working alongside Germany and France as well. I usually open toward Belgium when I play with Germany, which takes away the option of bouncing Russia in Sweden. If Germany is cooperative with England, that bounce will ensure that one of the pair can claim Sweden. In my mind, no matter what the case may be, a split in Scandinavia between Russia, England, and Germany in any combination will lead to inevitable conflict. I see England or Russia win that battle more often than Germany, but I've seen all three come out ahead.

Greece is a really interesting territory. For Austria, it's a monumental risk to take two units toward Greece. While that does assure that he will gain the territory, it runs the risk that Italy backsides him. I've never seen Austria recover from an Italian attack and survive Turkey and/or Russia and I doubt I ever will. I never leave Trieste during my opening moves as Austria, the weakest country, because to me, survival is key and to prevent a juggernaut, you can't wage war with Italy anyway. I try not to let an inexperienced Italy fall into it. In terms of Italian conquering of Greece, it usually ends up creating an Austrian war. Italy usually comes out ahead, but Turkey and Russia generally can crush him anyway. If Italy plays well enough, Turkey may stab Russia, and from there, the Italian/Turkish alliance is an excellent way to end up with 17 apiece. Still, I don't think one can shoot for that ending as it really takes a lot of effort and a lot of risk on the part of Italy. Turkey will only claim Greece in 1901 if nobody else goes after it. Simple as that.