ZGR is one of the hardest esn sponges on the market. @Michael Zhuang I'm not trying to dunk on you, but are you sure you weren't just hitting through the top sheet, but not hard enough to get into the sponge? Because of the hardness and tension of the top sheet, you really need to hit hard to even get into the sponge, let alone through it.
As to OP's question, after comparing Regular Rakza Z with ZGR and Victas V20 double extra, I would go with the Victas for FH. I haven't used RZ XH, although I assume it's pretty close to V20. The V20 sponge looks identical, and is listed at 53.5 and RZ XH is 54 iirc, and it already feels pretty close to RZ regular, just harder. In general, I find the V20 rewards good strokes more than RZ does, while the RZ is more forgiving of a mediocre stroke. I am keeping RZ for my backhand, where it excels for over the table play.
ZGR is honestly a little too hard for me to use, I lack the power to engage the sponge on every stroke, so while it may have the most speed potential, my shots are slower in game vs the other two.