Eventually, all players decide to equip their hero with a 7% set. There are many, but be warned, not all of them are the same. Depending on the hero setup you are playing (e.g. with low strength, or low brains, etc.) some sets may benefit you more or less. This is because the order in which skill bonuses are unlocked is not the same for every set.
For example, the Silver League set first opens the Intuition bonus (with 2 items) and last the Resistance bonus (5 items), while the set of the Righteous Fighter first opens the Strength and lastly the Intuition. This is of little interest to you if you play with a balanced hero setup. In that case you have to get a complete set (anyone) with 5 items to open the 7% bonus to all 4 skills equally.
But if you play with any other setup, then the order in which the bonuses are opened is important. Let's see the available 7% sets (in case I have missed any, please fill in), sorted according to the skill they open last. The parenthesis next to each set name shows the order in which the bonuses occur. The letters mean: S = strength, A = stamina, B = brain, I = intuition. Thus, the BAIS next to the Heroism set means that it first opens the bonus for Brain (with 2 items), then for Stamina (with 3 items), then for Intuition (with 4 items) and lastly for Strength (with 5 items).
Strength last:
- Phantom (BIAS)
- Flash Gordon (BAIS)
- Superhero League (BAIS)
- Antimagnetic (BAIS)
- Heroism (BAIS)
Stamina last:
- Silver League (IBSA)
- Gold League (IBSA)
Brain last:
- Bronze League (ASIB)
- Ironic (ASIB)
Intuition last:
- Champions League (SABI)
- Righteous Fighter (SABI)
It is obvious that if you play with a low-strength setup, it is better to use one of the sets where Strength bonus is last, and if you play with a low-brain setup, it is better to use one of the sets where Brain bonus is last. Thus even if you have only 4 of the 5 items in the set, the bonuses will be complete. You will have +7% in only 3 of the 4 skills, but they will be the ones you want.
But there is another very interesting option. Instead of using items of the same set, you can use a mixed set (3+2). That is to use 3 items of one set and 2 items of another. In this way you will again get 7% bonus to 3 skills and you can choose their combination.
For example, with 3 items from the Bronze set and 2 from the Silver, you get 7% again in Strength, Stamina and Intuition, as an alternative way to equip a low-brain hero.
Moreover, with a 3+2 set, you can give the 7% bonus to a skill twice, if you consider the particular skill critical for your setup. For example, if you want to greatly increase Intuition, use 3 pieces of the Silver set and 2 of the Gold (or vice versa). Thus, Intuition gets a 2*7% = 14% bonus and another 7% goes to the Brain (and not at all for Strength and Stamina).
Similar things apply to the 5% sets, but who cares for them nowadays? 
Mixed 3+2 set combinations can be helpful in designing your hero setups.
Enjoy,
DrSrDr
