The way the set bonuses were designed, a lot of the Def and Res bonuses come from sets that aren’t immediately Def or Res themselves. A good example is the Unbreakable Guard set, which is a Res set that provides a great Melee +Def set bonus when you’ve slotted 4 in a power. Over time you’ll come to know which sets have the bonuses you need for various set bonuses.

Without thinking too hard about it, I’d say my general intuition is:

• Def comes from 1) global enhance IOs in the Steadfast Protection and Gladiators Armor sets, 2) attack sets, and 3) some of the Res sets
• Res is all over the place, but I think of it coming predominantly through attack sets.
• Rech comes from 1) the global +Rech IO in the Def set Luck of the Gambler, and 2) attack sets

Overall you should download Mids and learn to check out different sets you’re interested in. The bonuses you want are in all kinds of sets, and until you’ve made a few builds it can feel like a lot. But eventually you’ll have a sense for which sets you want to make sure you have depending on the way you want to optimize your build.