From a purely functional point of view, I prefer the UN over the JLC because of several reasons:
1) The UN has a less cluttered layout, since it does not need a separate 24 hours display. It shows the numerical value of the home time in 24 hours.
2) The UN has a big date, the JLC hasn't.
3) The UN has a true quick-setting of the date, while the JLC only has a pseudo-quick-setting, similar to that of the Rolex and the IWC GST. When the watch has been lying unworn for some dozens of days, setting the date becomes somewhat a pain with the JLC, even if it is possible to set it backwards as well. With the UN, it is a question of a few moments, you can set it forward or backward.
In my opinion, not a single GMT construction of the recent years is coming really close to Ludwig Oechslin's ingenious invention.