None. Forget about sets for now. The set bonus is rather small, and trying to achieve this bonus by any means will lead to badly equiped champs. The stats of the single items are much more important. Later in the game, when your item pool is large enough, you can try to equip your champs with good artifacts from one set.
If the equip of your Galek is representative for the other champs, it illustrates very good what I mean. He has 3 complete sets, but his important stats are much to low. He is a damage dealer, so his crit rate should be 100%, speed, crit damage and attack should be much higher as they are. If you can increase his stats by sacrificing the set bonus, you should definetly do that. Use gloves with crit rate as main stat, chest armor with atk% main stat and boots with speed main stat.