The Maine Coon and the Ragdoll are at the same as far as size. Both are considered to be some of the largest. Someone might end up with a Ragdoll that is on the smaller size for its breeds standards or with a Maine Coon on the larger size...and vise versa. Its a good toss up.
I have two Maine Coons. My male is a not quite one years old and he is already 19 pounds and still has room to grow into. My female is of the same age and weighs 15 pounds also with room to grow.