Never used Leicas, because I was scared off by the price and turned off by the hype. But the one thing I do like about them is their very strong rangefinder spot. I shoot with Nikons and like them very much. They're rugged, reliable and affordable with a good selection of available lenses, but the diffuse, indistinct rangefinder spots are their biggest shortcoming, in my opinion.
Actually what is "strong" with the rangefinder spot of the Leicas are the rangefinder patch edges, and the rangefinder patch contrast
in comparison with the rest of what you see in the viewfinder.
BUT the Leica rangefinder patch is so bright that it works well for very contrasty subjects with very defined vertical lines so that you can focus quickly.
The shortcoming of the Leica rangefinder patch is that you don't really see what is inside the patch if your subject isn't contrasty.
And the Leica M4-2 / M4-P / M6 rangefinder patch flares very badly in any contrejour situation, making focusing almost impossible.
OTOH the Nikon rangefinder patch has fuzzy edges and less contrast versus the rest of what you see in the viewfinder, but allows you to see
what is in the patch very clearly, so that you can focus on an eye iris for a portrait with no problem. Added to the 1:1 viewfinder, this makes close-up portraiting a breeze. Just try this out with a 0.72 Leica...
The main shortcoming regards the original Nikon S3 viewfinder, which can flare a lot due to desilvering over time, hence a RF patch with so little contrast than focusing gets very difficult if the subject isn't very contrasty.
As Erik said, the Nikon S2 rangefinder patch might be the best you can find on any RF camera, period.
Some people like to remove the square mask off their Nikon RF camera rangefinder secondary front window. I tried this out but didn't find that it brought any improvement.