Many of the Tuners have useful effects, such as Synkron Resonator which will add another Resonator from the graveyard back to the hand when it's sent from the field to the graveyard (which is easy to do with Synchro summoning)
With all sorts of ways to tap down creatures, with cards like Sleep, Opposition, and Timin, Youthful Geist, you have a plethora of cards to not only lock down your opponents, but to provide tons of board presence and card advantage over the course of the game
I appreciate them for what they are, but running them for two straight generations really burned out the collector base
I give the nod to cards that can generate mana of any color, or in the case of EDH, any color in that commanders color identity
Feldon's cane: Odd to see it there at first, but in a much slower environment, this allowed players to reuse their restricted cards a little too much