Recently, Augment Code. But more generally, the "leader" switches so frequently at this point, I don't commit to use either and switch more or less freely from one to another. It helps to have monthly subscriptions and free cancellation policy.
I expect, or hope for, more stability in the future, but so far, from aider to Copilot, to Claude Code, to Cursor/Windsurf/Augment, almost all of them improve (or at least change) fast and seem to borrow ideas from each other too, so any leader is temporary.