The honest answer first: no kit is better for coding than the others. They all run the same way — you code them in CircuitBlocks, which writes MicroPython and works identically on every device we make, with C++ available at firmware level if you go deeper. The details are in What programming languages can I use with CircuitMess kits?
So the question worth asking is not which kit teaches coding best, but what your coder would enjoy programming. That is what changes between them:
Something that moves and sees. Wheelson 2.0 is a self-driving car that navigates with a camera, so the programs you write are computer vision running on the car itself. Recommended for ages 9 and up, about two hours to build — see CircuitMess Wheelson 2.0 — Frequently Asked Questions.
Something that talks to a friend. Chatter 2.0 is a pair of communicators that send encrypted messages over LoRa radio with no Wi-Fi and no mobile network, so the programs are about wireless communication. Ages 9 and up, and you build two units — see CircuitMess Chatter 2.0 — Frequently Asked Questions.
Games and a console. ByteBoi 2.0 is a handheld console you build and then write games for. Ages 11 and up, about an hour and a half — see Build time, tools and recommended age for ByteBoi 2.0 and Wheelson 2.0.
Music. Jay-D 2.0 and Synthia 2.0 turn coding into sound, mixing and effects.
Choosing between Chatter and Wheelson — the pairing we are asked about most — comes down to that difference alone: both are ages 9 and up and take roughly the same time to build, and both are coded in exactly the same environment. Wheelson suits someone drawn to robots and cameras; Chatter suits someone drawn to radio, messaging and building a matching pair with a friend or sibling.
If age is the deciding factor rather than interest, Is there an age limit for using CircuitMess kits? lists the whole range, and The Perfect STEM Gift of Choice — Frequently Asked Questions is the gift-buyer's version of this question.