Defender of Argus
Great for protecting yourself and other minions. Note the positional aspect of the Defender. You can place it in between minions and give them both taunt or place the Defender at the end and only give one minion taunt (and provide a blocker for the other if it's more valuable, such as a Knife Juggler). Pretty solid value considering he comes in with 4 mana and is a mid-range minion with 3/3. Great for heavy minion decks like paladins or shamans.
Not only does the Knife Juggler come out as a 3/2 for 2 mana, the little gnome knife chucker practically comes in with a built-in taunt! I've rarely had this little guy last for more than a turn! He usually gets blasted away before he can start juggling knives at all. But that's the beauty of it as he'll draw a removal spell early on. If he doesn't, hopefully you can whip out some other minions and take advantage of his triggered ability. Great for minion decks mostly.
You can't buy a Knife Juggler without an Imp Master. This generator of Imps is a guaranteed 1 extra damage per turn in tandem with the Knife Juggler until it dies. It'll slowly wither and die away turn after turn. The Imp Masters health pool is high enough to help weather and trade with any smaller minions your opponent has on the board. Even though the Imp Master starts off as a 1/5, you can use a variety of buffs to help sustain the generation of imps. Giving it Divine Shield will also create an extra imp since the Imp Master has to take damage and not actually suffer any health loss. Would only pair this with Knife Juggler decks.
The drake is a staple in just about all spell related decks. Most mage decks will want to utilize it and I've seen certain rogue builds include it as well. It'll draw you an extra card, too. The 4/4 renders it immune to some of the priest spells and that 4 health is going to keep it alive against most board clearing spells. Tough drake! The drake does cost 5 mana so you'll have to wait a few turns before you can cast it.
Looking to develop a combo deck? The auctioneer is practically a requirement. This goblin is the engine that will keep your deck going and help you draw into the minions or spells you need to seal the game away. Just like the Azure Drake, the 4/4 means it'll provide some toughness and allow it to dish out some pain.
This Drake in particular is weaker compared to the original iteration (where it would gain +1/+1 per card in hand). Despite that, it guarantees you 4 damage when it drops regardless of how big or small your hand size is. I wouldn't recommend using it late game since it isn't likely you'll have that many cards in your hand. Try to get it out as soon as possible. Turn 4 is the earliest you can get it out (unless you have The Coin). Decent in control or spell heavy decks where you'll have many cards in your hand. I highlighted this card a while ago.
The Cobra (like the Knife Juggler) is also fairly high on the threat board. Reason being is that the Cobra will trade with just about anything that doesn't have a Divine Shield. The Cobra will bring down even the mightiest and toughest of minions regardless of how large their health pool is. Hunters might want to consider including the Cobra since it's also a beast type (which synergizes really well with their theme). Really good for hunters but is a decent pseudo-removal card in any deck.
Doesn't seem like much at first glance. Who wants a Blademaster that deals 4 damage to itself right away? Well, priest decks can mitigate it easily enough with their hero powers. Warriors love him since most of their cards have abilities that trigger off of damaged minions. Besides, 3 mana for a 4/3 is nothing to snooze at. Best played in warrior or priest decks.
Last (and probably least, depending on who you ask) is the Pint-Sized Summoner. You'll run into this card in certain aggressive decks. I use it myself in my warlock Murloc deck. Unfortunately, the Summoner is a 2/2 and often isn't durable enough to withstand trades. Most opponents will be willing to trade their smaller minions for it because if they don't, they can expect you to whip out your later minions one turn earlier. Used for decks that rely on overwhelming the opponent.
At the end of the day, if there's just one card you can craft, make the Argent Commander. Two copies of that in your deck will help you immensely when it comes to trading or opening the way for the rest of your minions.