I'm just an idiot on the internet and don't pretend to be anything else, so with that in mind here is my opinion.
In order of importance...
Is the tip the same brand and same shape and same length as the tip on your other cue? The tip is the only part of the cue which actually makes contact with the object ball, changes in the tip will affect your game. A lot of players stick with the same brand and immediately sand it to the shape and length they are comfortable with.
Is the ferrule made from the same material and the same diameter?
Is the shaft the same diameter and same taper?
farther down on the list are the balance point, weight and joint type.
In order of importance...
Is the tip the same brand and same shape and same length as the tip on your other cue? The tip is the only part of the cue which actually makes contact with the object ball, changes in the tip will affect your game. A lot of players stick with the same brand and immediately sand it to the shape and length they are comfortable with.
Is the ferrule made from the same material and the same diameter?
Is the shaft the same diameter and same taper?
farther down on the list are the balance point, weight and joint type.