First Tier, 60-70% of your games and study time:
1. KID / Benoni, Hungarian, Seirawan (Bd3), or Four Pawns
2. Nimzo, Reshevsky
3. QGD, Exchange (pt.1, pt.2, pt.3, pt.4, pt.5)
4. Slav, Exchange
Defenses in the First Tier are common enough to justify playing a relative mainline. Proponents of these venerable defenses are usually very experienced to have seen everything before and not to fear big theory. To promote efficiency I only considered anti-KID variations that apply equally to the Benoni so as to kill two Angry Birds with one stone. I also settled on the Exchange Slav to avoid the labyrinthine Slav and SemiSlav.
Second Tier, 20-30% of your games and study time:
5. Dutch, 2.Nc3
6. Grunfeld, Romanishin
7. Benko, Dlugy attack 5.f3
8. QGA, 3.e3
The Second Tier defenses tend to inspire fanatical devotees at the club level, who thanks to excellent repertoire materials for Black tend to be fairly knowledgable and booked up. So I purposely went for sidelines that strike me as being atypical for the opening and/or easier for White to play intuitively.
Third Tier, 10% of your games and study time:
9. Budapest / Fajarowicz gambit (pt.1, pt.2)
10. Tarrasch / Schara gambit
11. Chigorin / Albin gambit
The Third Tier defenses generally rely on early tricks and/or early confrontation in the center. As a result, the play is generally very forcing from the get go, meaning that Black has few ways to deviate from established lines without just being clearly worse. In turn, it is relatively practical to prepare a reliable line fairly deeply since Black's responses are predictable and limited.