I find z2 extremely grippy, dignics level, and doesn't react strongly to spin. It throws the ball a bit lower than g1 too. G1 is also very grippy, but not as much as z2, it also bites spin more. G1 feels safer when doing topspin shots because it has a higher arc, but z2 grabs and spins the ball just a touch easier.
It's what you prefer. For me the z2 is a rubber for close offensive play and blocking. The g1 is an all out attacking rubber that likes mid distance and first topspin at backspin pushes. You can also put more power into the g1 due to that arc, the z2 may fly long a bit easier.
When I used a racket with both on it, I liked the g1 on the fh and z2 on bh. Nowadays I would probably put z2 on both sides, but keep in mind, it's a bit heavier than g1. I would say ~2 grams up from the g1. It's not a big deal though, marginal difference, could be down to the individual rubbers.