Tier 1: Easily effective
This group of Heroes are easy to play and easy to be effective with. They will excel at one of three things: (1) simple kill power against enemy Heroes (2) wave clear (3) killing buildings / objectives.
Tier 2: Decent
All of these Heroes are fine. Comfort level matters.
Tier 3: Best avoided
These Heroes generally have stronger equivalents in the Nexus, or they require certain conditions or skill sets that are more rare in Bronze to Gold. Finally, many of these will tilt your allies upon picking.