WiX v4 is the latest version of the WiX Toolset. At FireGiant, we recommend upgrading as soon as possible and offer conversion services to help you out. We also provide HeatWave to provide an integrated experience with Visual Studio.
While WiX Toolset v3 is the most widely used version of the WiX Toolset, we do recommend upgrading to WiX v4. But we also know that upgrading can take time. And some products may simply need to stay on WiX v3. At FireGiant we offer FireGiant WiX v3, which is fully supported by our Enterprise Support Program and includes additional functionality that can make you more productive using the WiX Toolset.