Spears > cuttas due to range. Your goblins are not the tankiest infantry bricks in the game, so the design seems to be to field huge numbers of them to drown the enemy in save rolls - they're bound to fail them sooner or later! the spears having an extra inch of reach allows you to get more of your men within reach to contribute attacks during the combat phase and sort of offsets the otherwise poor To Hit chance per model.
The thing about fielding goblin bricks though is their whole "bonuses to wound if there's more than 20 of us" mechanic: these troops won't hit very often, but they can make sure anyone they hit stays hit. I will repeat however that they don'w have much staying power and will be taking awful (and comical) amounts of attrition over the course of the game. The best you can do though is to put the full command group in each mob and laugh at enemy non-artillery ranged units as they fail to cause unsaved wounds (6+ base save, 5+ for shields and 10 or more models in the unit, 4+ save with mystic shield from a friendly wizard, 3+ save total for all the above and the moon banner versus shooting attacks) while the flag waver makes your troops less likely to fail battleshock tests if they aren't locked in combat.
Overall a decent Distraction Carnifex that can hold long enough for your actual heavy hitters to reach the front (or shatter all expectations by doing their job for them).
Skarsnik is indeed one of the better models you could use for the warlord, given he has a multi damage weapon to deal with tough gits, an extra weapon to add insult to injury, and a couple of ranged attacks as well.
Squigs, especially in large numbers and/or the manglers are also a sound choice provided you use the blobs effectively to dispose of enemy rangers, cuz the walking rugby balls with teeth are about as glass cannon as you can get without being an elf. In short: take squigs in bulk or not at all.
You could use your allies area for as many goblin artillery units as you dare. many will swear by the bolt thrower for it's anti hero ability, but I personally get mileage out of the rock lobber. 3 damage is 3 damage, especially if it's coming from the other side of the field from turn one.
Just make sure that your money maker units are nicely protected by lots of chaff and bubble wrap to screen them from nasty deep-striking Sigmarines and anything that flies. Hope this helps in any way