You have to reach WAAAAAY back and overlook his, ahem, interesting character quirks compared to social mores of modern culture, but Utter got it right, it's Cap Anson, and by a long measure.
ps. He was even better than Ernie. Truth cannot be heresy.
He was a terrible person but a pretty good ball player....Cap Anson.
edit: If you're talking about the best player that played for the Cubs then Rogers Hornsby would be the choice. However since you said "best Cub" then it's tough to include Hornsby as many players had better careers as Cubs. Hornsby's two triple crowns came as a Cardinal and he only played 317 games for the Cubs batting .350.
Ryne Sandberg
Ron Santo
Gabby Hartnett
Billy Williams
Out of these, I'd have to go with Billy Williams as far as regular lineup players. And these pitchers also should be recognized:
Fergie Jenkins
Greg Maddux
Of these, I'm taking Maddux so I would say Williams as thje best full time player and Maddux as the Cubs best pitcher.
Ron Santo
Even though he did not play with the Cubs, I would have to say the late Harry Caray.
sandberg./.
