The primary abilities, huh?
You should probably use whatever works best with your weapon, but for some general suggestions;
For headwear, try Special Saver (so you don't lose all of your special charge when you get splatted), or maybe Special Charge Up or Tenacity (they both charge your special up faster, which is good), maybe Special Duration Up if you've got a special that works until the meter empties (Kraken, for example).
For clothing, Ninja Squid is great if you're not using a Charger (no need to sneak around if you're sniping). If you are using a Charger (or maybe a Dynamo Roller, they can kinda do sniper stuff with their HUGESWINGS), go for an Ink Saver (Main if you don't use your Sub Weapon much, Sub if you do), or maybe Ink Recovery Up (to restore ink quickly).
For footwear, unless you're using a Charger, you NEED Ink Resistance, it'll save your life. If you are using a Charger, perhaps consider Swim Speed Up (for getaways) or one of the Ink Savers or Ink Recovery Up (see above).