Open a new image
Create an anti-aliased selection: For example, an elliptical one.
choose an even number for the stroke width.
From the Edit menu, choose "Stroke Selection".

the resulting stroke is jagged: there is almost no anti aliasing, despite the
"antialiasing" option being checked.
choosing an odd size for the stroke makes it somewhat better.

The problem seems to result from lack of sub-pixel sampling in the stroke
process. Using odd brush sizes aleviate the problem somewhat since the stroke
edges receive 50% stroke only (the odd pixel is devided between the two sisdes
of the stroke).

Since this is tested on 2.2 pre-1 this may have something to so with bug #157102