Goblin Guide: One of the best one drops we can cast. This card has some pros/cons to it. Being that an opponent can draw some extra lands (Pretty much free cards). However, if the card revealed isn't a land, it gives us added information about what they are drawing into. Slamming a Goblin Guide on turn one isn't always the best play. Foundry Street Denizen is what you want to be playing first. After turn one, this will net you more damage.
Foundry Street Denizen: If this is in your opening hand, make sure this is the first Goblin you cast. He doesn't have haste, but after turn 1 he will always net you more damage than playing a haste creature turn 1. This is because he is pumped by other Goblins entering play.
Frenzied Goblin: This Goblin is a flex spot. There will be a few situations in which you'll want him, but he is not that important. He is great at pushing through extra damage if you're in a board stall.
Goblin Bushwhacker: Once again we have another Goblin here that you'll always want to be kicked. This makes the deck so much more explosive, thus getting in even more damage.
Goblin Chieftain: This lord of the Goblins adds explosiveness to the deck. You do not want to be attacking with him if you fear removal or enemy blockers. If he dies the entire team will become weaker. He isn't great in removal heavy matches, because he is a magnet. However, he is effective against combo decks. If your opponent is racing you and you're racing him/her, you'll want more lords.
Goblin Piledriver: The Piledriver is used for trying to do extra damage to the opponent with only a few goblins. This goblin is only at its maximum potential if he has a team of goblins behind him. So you will not want him in removal heavy matches. He is great against combo decks or aggro decks with light removal. Against Merfolk, he is somewhat relevant until they achieve Islandwalk.
Legion Loyalist: This is a Goblin that is super effective against token strategy decks. He is also good against the decks with lower toughness creatures, which would be Affinity/Infect/Burn/Melira Company.
Mogg Fanatic: This Goblin is used to take out important low toughness creatures. A few would include anything from Affinity/Infect/Melira Company or even a Dark Confidant. He is the perfect chump blockers as well. Bring in a full playset of him against the mentioned decks above.
Mogg War Marshal: The Marshal is a token generator that has great synergy with the rest of the deck. One example, he can pump Foundry Street Denizen multiple times. Adding multiple creatures to the field for a two mana is pure value.
Reckless Bushwhacker: You will always want to playing the Reckless Bushwhacker for its surge cost. This means you cannot empty your hand immediately. You must save at least one other spell to get maximum value out of this card. When he comes down, its for a large powerful swing with the team.