To me it's all about overall importance to the franchise. That combines on-ice contributions, team accomplishments, and post-retirement presence. Bathgate really sags in the last two categories. Cook excels in the first two categories, but not in third. He coached the Rangers for a couple forgettable seasons in the 50s.
Leetch and Messier have to be there. They were great players on the ice, were the two biggest factors (along with Richter) in bringing the franchise its only cup in the last 72 years, and they remain big presences within the organization.
Boucher has the Hall of Fame credentials, the two cups as a player, and he coached the team to its 1940 cup win. He also served as GM for many years.
Gilbert's a Hall of Famer too. The GAG line and Park teams led the Rangers to relevance for the first time in 20 years. Say whatever you want about adjusted points, but being the team's all time leader in goals and points is a major factor. Nobody's even close to him in total goals. Leetch is the only guy who's close in points. Both the fact that Gilbert was the first Ranger to have his number retired and his continued presence as a team ambassador speak to his prominence within the organization.
I'm not saying that Cook and Bathgate weren't great, great players. They were. They both had great stats and Cook even won two cups. But their overall impact on the shape of the Rangers as they stand today doesn't measure up to the four I picked. If this were a measurement of importance to the overall history of hockey, then Cook and Bathgate would rank higher than Gilbert. But we're talking about the Rangers here, not hockey as a whole.
Andy Bathgate and Bill Cook are easily the best players to wear Ranger jerseys.
We'll just have to agree to disagree, since we are clearly using different criteria.