This ColourfulStacker is a great one for encouraging hand-eye coordination. Children learn to discriminate objects by size.
Initially, the baby may simply remove the rings and need help to stack. You could then remove some rings and start by offering two rings to stack and then more upon mastery. It may take some time before they stack according to size.
The wobbly base means the child will not knock it over as easily and is more set up to succeed. Later you can introduce a stacker with a stable base.