frankly, they are all the same. They are excellent though, and my favorite mushroom. I suggest, instead, that you get one warm weather fruiting variety, and one cold weather fruiting variety. I have the cold weather one, so I get to eat them only in early November.

Kings (pleurotus eryngii) taste different from the others and is my favorite tasting oyster, it is a lot like eating a wild boletus. However it is more fastidious to grow then the other ones and may not produce unless the conditions are just right.
The other oysters are really easy to grow. I have cloned them from supermarket mushrooms with no problems, they also taste pretty good and are one of my favorite mushrooms.
Last have you tried Stropharia? They are extremely easy to grow and make a lot of big mushrooms. The taste of Stropharia was a little bit different at first, kind of like potato, but really grew on me after a season.

Yes, I agree that king is different, but not a real oyster culture-wise. I think it is a mediterranean fungus, and not really well suited for the colder parts of the US (which, compared to the mediterranean, is 95% of the US).