Player rankings are almost always subjective. The very is inherently based on opinion from so many voices and in that light, debate can stem from any general list. Since there is no consensus outlet on these kinds of analysis, it's difficult to figure who one would consider the best current Chicago Bears.
Just take a gander at the present options of player rankings.
Sure, to decide on the best Bears of the past and future, you could look to the Hall of Fame, but that voting can be convoluted and drawn out over time. There's the NFL Top-100 list, but its been pointed out that this annual list should have no merit and isn't taken seriously at all by active players.