Your question really doesnt make much sense because if you collect decks then it really doesnt matter as the idea is to get many different decks.
However if you mean rare then there are jerry nuggets, blackghost 1st edition, brown sealed wynn decks and pretty much any deck that is hard to come by.
A good start in card collecting is to just get a lot of various decks that arent out of print yet but not everyday decks like theory11s decks, ellusionists or just strange different bicycle decks eg. silver deck, yellow ect.
Just have a look around on sites there are many. I like ace king on ebay give it a try.
Hope I could help.