I agree with daisukeman. I went for sets 3 and 8 last time because you have the best shot at getting game-changing cards. I feel like going for base sets (1, 4, 7) is pointless due to the huge number of useless rares, but it seems like you guys have had good luck with those.
Okay, I'd like to focus on the Series 1 starters for a bit. As a reminder, the three options for Series 1 are:
Deck 1: Gandalf/Shire and Southrons
Deck 2: Dwarves/Elves and Dunland
Deck 3: Gondor/Rohan and Uruk-hai
Disregarding booster pulls, deck 3 for sure. Only downside I see to that deck is twilight generation from FP side, and maybe some man hate from Raider cards.
I thought a lot about this, and spent some time looking through all of the card lists. Your point, I feel is only true to the extent that sets 3 and 8 have smaller card pools so your chances of pulling one of the rares that you
want is slightly greater. However, the base sets, after looking at them don't have a huge number of useless rares at all. On observation of Set 1.
The only that I would consider completely useless rares that I found were (and some might argue):
Mithril ShaftThe Council of ElrondThe Nine WalkersAn Able GuideArwen's FateThe Choice of LuthienAlive and UnspoiledCruel Caradhras Saruman's ReachUruk SpyCave Troll's HammerDenizens EnragedThe End ComesFool of a Took!Goblin DomainLost to the GoblinsThe Underdeeps of MoriaIn the Ringwraith's WakeThe Twilight WorldDespairThe Irresistible ShadowJourney Into DangerMordor EnragedOrc ButcherySeeking its MasterThe Weight of a LegacyThe number of usable cards from set 1 is actually huge, and a lot of them are really great. This is because of the fact that throughout the choice of the three starter decks each serie, you will more than likely have access to a vast array of the "main" companions, and not just fillers. Any of the rare companions are good. Their weapons are great too. Not to mention the allies.
Galadriel, LoL, or
Albert Dreary are clutch. Take a look at the rare Isengard cards too. Aside from those few events, those Uruk cards are great, especially considering how strong Uruks are in this league.
Altogether I counted 65 cards that would be great pulls from Set 1, as compared to 26 really bad ones.
For Set 3, I found the following cards to be either utterly useless, or dependent on pulling another rare (like
Vilya or
Nenya...chances are you won't also get Galadriel or Elrond, so don't count on it being a useful card)
Book of Mazarbul Mines of Khazad-DumForests of LothlorienNenyaVilyaThe Shards of NarsilCitadel of Minas TirithA Fell Voice on the AirHollowing of IsengardDepths of MoriaGates of the Dead CityHis Cruelty and MaliceMorgul SlayerOrc TrooperTerrible as the DawnWhy Shouldn't I Keep It?Melilot Brandybuck, Merry DancerThe Shire CountrysideDoing the same comparision, I found 15 good pulls from Set 3 (and I'm even including both of the Tower cards - one adds twilight, the other assists in getting initiative), up against those 18. Just as in Set 1, I left out some cards that appeared to be neither really bad or really good, and depend on your deck type (like the Set 3 Arwen or Set 1 Cave Troll).
You can just by the percent ratios, you actually have a better chance at getting an at least usable rare if you go with set 1. Yes, going set 3 gets you a closer shot at the rares you want, by the card pool, but its a risk since there's still an even greater chance you end up with garbage.
I'm looking at set 8 right now, and I'm having a hard time seeing these "game changing" cards that are actually as strong as Set 3's Palantir or
Horn of Boromir. Half of the cultures' cards aren't going to help you at all (look at Gondor and Dwarf for example). Really Sauron is what is actually good, with an easy chance at a
Great Hill Troll, and a long shot chance at a Grond. Still, I don't find the balance staggeringly in favor of it.