Can you give more specific criteria than “best?”

Visual Studio seems very popular and has everything one needs for writing and debugging C code, but only runs on Windows and costs money.

vim + git + gcc + make + gdb another popular set of tools, more portable and free.

The “best” environment or set of tools will depend on your skills and patience, and likely on the kind of development you intend: embedded code has different constraints than desktop application code, for example.