Hard to determine 'best.' They all have pros and cons. (I won't include potential electronic failures or repairability as a con.)
I have owned a ZM, multiple CLE, and multiple Hexar RF film cameras over the years. Never have used Bessa/Rollei so no comments on those.
Quick comparison:
CLE:
--Pros: size, weight, exc. 28mm view, quiet shutter, small cheap ubiquitous batteries.
--Pro or con depending on what focal lengths you prefer: 0.58x magnification.
--Cons: no 50mm frame, no manual metering, shorter baselength (but who is going to attach a Noct on a CLE anyway?)
Hexar RF:
--Pros: 1/4000, built-in wind, 1/125 flash sync.
--Pro or con depending on what focal lengths you prefer: 0.60x magnification.
--Cons: CR2 batteries.
ZM:
--Pros: 1/2000, viewfinder (solo 35 and 50 frames), exc 28mm view, focal length indicated on the frameline, light weight, small cheap ubiquitous batteries, long RF baselength, 1/125 flash sync.
--Cons: RF patch doesn't move with parallax correction, weird AE lock location/operation
I'm quite happy with any of these cameras, they all get my vote. 😎 Although it appears the CLE has the pricing advantage, followed by the Hexar RF, and the ZM is getting 'up there' in price.