Primary has a fair amount of certainty to it. It's either success or fail, first item is the base, +4 max. It's simple, which is why it still has its uses despite the abilities of Junior and Superior.
Junior is useful for the fact that a 'complete fail' is rare; usually I've seen the base item returned or a decrease in rank. Rarely have I seen common stones/straw mushrooms/etc. However, when compounding some items, as an example a thorn suit, Junior cannot be trusted. It fails at an astonishing rate, my primary at that level did not have such an issue making them. Although, junior's "rank +1" by default law comes in handy also.
Superior is once again success or fail, and does have an increased rank range. It tends to have a high success rate, making it fairly reliable. It's Superior for a reason.
All in all, I'd have to agree with dotnet. Primary and Superior, though Junior has its uses.
Guy 1: "Hey, see that car?"
Guy 2: "What car?"
-screeeech-
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ign = Kazura
Server = Cancer 2
Element = Fire