I'm sure a popular choice is a starknife with the called fusion. Who wouldn't want the Glaive from Krull?
Starknives. You need to spend a separate feat on Special Weapon Proficiency to become proficient with carbonedge shuriken, and they become obsolete pretty quickly. At least there are higher-level starknives.
Definitely the starknives.
There are three special weapons you can take proficiency with in the core book, and I don't understand the point of two of them, as they both have a level 1 weapon, then stop. The net, sure, why not. The bow, I can kind of see scaling with grenade arrows.
But carbon edge shuriken? They let you trade range for a crit effect at level 1, then just stop.
If you want throwing to be your thing, then even at level 1, you can afford to buy one and put the returning fusion on it, letting it be both your ranged and melee weapon. It would cost more to keep a stock of shuriken. You could put returning on shuriken, but that's also cutting into their cost-effectiveness.
About the only utility space I'm seeing for shuriken only exists at level 1, and only if you really want to full attack throw right out the gate, and you're a human spending your two starting feats on shuriken proficiency and multiweapon fighting.