The unlimited will initially have a print run of 100,000,000 cards with more if necessary. Later printings will rotate cards from the expansions into the unlimited set. Finding Limited Premiere packs is near-impossible now. There are also location cards, representing sites from the trilogy such as Mos Eisley's infamous Docking Bay 94, or the ill-fated Alderaan system. Uncommon cards are often more central to the trilogy - incidental characters such as Jek Porkins, powerful weapons like the lightsaber and larger starships such as Imperial Star Destroyers are typical uncommon cards.
Rare cards are the most important cards.
However, although you get more cards for your money in a starter pack, there is a much lower proportion of the rarer cards. A starter deck contains only 2 rares in 60 cards, compared to 1 rare in all boosters. A booster also contains a higher ratio of uncommons when compared to a starter pack. The expansions are only available in booster packs, which contain a set number of cards in a specific ratio of rarities. The first three, entitled A New Hope, Hoth and Dagobah are now available.