First you should decide, if you really need a coupled rangefinder or if an uncoupled one meets your expertations.
Coupled rangefinder:
+ more precisely
+ a bit faster in operation
- more weight and bulk (most time)
- more expensive
The difference in operation of an uncoupled rangefinder is that you determine the distance with the rangefinder and transfer it to the scale at the lens. In this case you should check if both scales are in feet or meter so that you don't have to do the math before each shot. It is also benefical for faster work if the scale has the same increments at both scales.
An alternative to a uncoupled rangefinder is using a rangefinder in the accessory shoe.
Here a picture of my Agfa Record II with Voigtländer Rangefinder:
IMG_4229 von
thomas.78 auf Flickr
In both cases you should not only consider the type of lens (and shutter) but also the ergonomics ot the campera.
(automatic film advance, double exposure lock (or not),
operation of the shutter release (left or right hand, at the body, door or the lens), focusing method, how you have to hold the camera, combined viewfinder or not, ...)
They also have a different minimum focusing distance, normally between 1.0 and 1.5 m.
If you can tell us your priorities, it would be easier to make you suggestions, which folder might fit you.
P.S.: Which Zeiss folder do you use ?