I bet it's the VX-III, but of course IDK.
IME, the Super Slam series is significantly 'better' optically, in terms of subjective brightness and image 'pop,' than the current VX-3. However, the Leupy's eyebox is more forgiving at max power (4.5 - 14 vs Weaver 3-15), and possibly in general.
The Grand Slam, however, has quite a bit less eye relief. Whether that's important or not is specific to the shooter and the rifle. Optically, the _previous_ Grand Slam seems similar to maybe not quite as good, but I never had them side-by-side as I have with the Super Slam series. I have also performed NO instrumented tests on any of them, so everything about image quality is subjective.
As goodshot says, each has its strengths. Leupy's support is definitely one of its strengths. Weaver will also support their customers, but in a different way and on a different timetable these days, IME.
