Difficult one to answer, much depends on your background and requirements.
Be aware though that both Studio and Atelier are effectively end of life, with Intersystems only releasing critical fixes, and VSCode ObjectScript is not an Intersystems supported product. The Serenji VSCode plugin has its own support but is a commercial product.
Despite requests here and in person to various levels at Intersystems they won't provide any plans for development tools which muddies the water somewhat when trying to decide on a toolset.
If I were starting from scratch I would pick VSCode and try out both the ObjectScript and Serenji plugins as these are at least in active development and have better flexibility and support for other third party tools such as GIT and Docker.