RW - with lots of burn and lots of goblin tokens. Between all of the burn and Chained to the Rocks, you have tons of removal to clear the way for your goblin swarm. Soulfire Grand Master is primarily for the lifelink attached to your burn, but in late game - or with a convoked Stoke the Flames, you can easily buy it back. Chandra, Pyromaster, Outpost Siege and Commune with Lava all provide some card advantage, after you've emptied your hand somewhere around turns 5-6. Outpost Siege can pull a double duty - if you're not hurting for cards yet still have a decent swarm of tokens with no way to get them through, you can go dragons and suicide your goblins against their walls to squeeze in that last bit of damage. 9 times out of 10, you'll go Khans to get that second draw every turn.
After playtesting with a variety of competitive decks, I've made some tweaks to the sideboard. Mainly adding Monastery Swiftspear and Scouring Sands in place of the weak Dragonlord's Servant and squeezing out one Draconic Roar.
Playing vs nearly any midrange is fine as is. The toughest decision will be whether to burn the opponent or his creatures.
When playing vs Sidisi Whip or any midrange aggro featuring black, board out all Goblin Rabblemaster and Hordeling Outburst, and board in all Thunderbreak Regent, Stormbreath Dragon and Draconic Roar for game 2. Taking out onesey-twosey stokes or strikes to make room for the roars. The roars make a good replacement for lightning strike so long as you have a target, and the stokes aren't as effective without a goblin swarm to convoke them. Siege Rhinos are tough, but you should be able to chain them to a mountain or kill with a combo of Lightning Strike
+
Wild Slash
if you're desperate. With some luck, your opponent will board out spot removal in favor of Bile Blight and Drown in Sorrow - which will do no good against the dragon power you're packing now.
Playing vs any kind of sligh - monored or red/green gets a little tricky. You want max cheap burn to pick off his early attackers while keeping your goblin swarms to meet his head on. So board in your Draconic Roars and Scouring Sands, in favor of end-game card advantage like Commune with Lava, or heavy burn like Stoke the Flames. Even without dragons in your hand to trigger the Draconic Roar, it will still kill anything he puts on the battlefield, and you need to pick off his threats as soon as they land. You'll still have Chandra, Pyromaster and Outpost Siege, so once you've ground down his offense around turn 5 or 6, you can take some card advantage and finish him off.
Playing vs control - whether UB or UBW - you need to come in fast and early and hurt him as much as possible before his mana-hungry lockdown can take over and lock you out of the game. Board out Chained to the Rocks, which will do no good vs the hexproof dragons he's rocking, and board in your Monastery Swiftspear and Thunderbreak Regent. A turn 1 Taylor Swiftspear gives you a good shot at burning him out before lockdown. Throw all the burn you have straight at him, hopefully triggering prowess on swiftspear and seeker. He'll have to either counter your thunderbreaks or sweep them to avoid the strike effect, which should bait away some of his counters for your gobbies. Having goblins and dragons on the field at the same time will make for a tough choice when he comes sweeping with crux of fate. Stay on the offense and keep him reacting, and you've got a good shot at it. If it's late in the game and he's managed to stall you out, wait until the last minute with a few burn spells in your hand to crack out that last bit of damage: he's bound to counter the first one or two - so try to get him with the third.
