For starters, all four of these blends are stellar products. In fact, those four blends represent, to me at least, 2/3 of the renaissance in classical style latakia blends that we've been blessed with over the past few years.
Black House is probably the most popular (though not my favorite). It's a very robust balkan-type mixture with lots of latakia and a subtle sweetness. This stuff has developed a cult following (do a search and you'll see what I mean).
Magnum Opus is my favorite of the lot. It's a very, very complex mixture that is definitely in the classic "Balkan" camp, which means that the focus is on the orientals. This is a very complex blend that responds well to large bowls. Russ Outlette apparently managed to score some truly remarkable oriental leaf for this one.
Both Wilderness and Legends were made by Fred Hanna, who is something of a legendary figure in the pipe smoking community. Legends is a fairly traditional latakia blend. Due to the dark stoved VA, it has a rich sweetness that you won't find in many other mixtures. While the orientals are prominent, I feel they are balanced out by the latakia. Wilderness, on the other hand, is more of an oriental or Balkan mixture. The focus here, like in Magnum Opus, is definitely on the oriental leaf. McClelland has an impressive stash of orientals plus Syrian latakia, and both are used to good effect here.
The one complaint I have about Hanna's mixtures is that, like all McClellands, they are very mild blends. Exceptionally mild. Ridiculously mild, even LOL. I like a lot of body and nicotine in my smokes, and they are simply too light for me. But if you don't like powerhouse blends and do like latakia, I would recommend these two above everything else on the market.
Another couple of new blends that you might want to look into that are on par, quality-wise, with the above mentioned four are:
Fusilier's Ration: This is Oulette's version of the venerated Bengal Slices. I've not tried the original product, but this stuff is almost supernaturally tasty. It's basically a rich Balkan mixture that has been pressed and infused with a light topping. It's utterly unique and, to my taste buds at least, an instant classic.
Also, GL Pease's Gaslight is one you should try. It's another five-star latakia mixture, this time pressed into a sort of cake or plug.
In any case, I don't think you could go wrong with any of the blends mentioned.