Yeh personally I'm not a huge fan of the grooved and scored foam cores, they do end up quite heavy. Depending on the application, 3D PET core can be better because it only uses about 300g/m2/mm. I prefer it for relatively thin applications. Once you start getting to like 10-15mm core thickness then I wouldn't use 3D PET core in any stressful application as it will shear from itself, so that is where the PVC cores come into their own.
Another alternative that I'm a big fan of is Corecork. There are 2 densities, the heavier NL20 uses less resin while the less dense NL10 uses a bit more, so 2 identical panels will turn out close to the same weight. The NL20 uses about 200g/m2/mm and the NL10 is around 170/m2/mm. So can be substantially lighter than foam cores, but their compressive strength isn't as high.