resurrecting a long lost thread but I just recently came across the need to implement "wantsBestResolution" and the Starling library, as of now, does not implement it, since contentScaleFactor is in fact a (slightly) different beast.
I ran in to an issue where a 2X texture would render super blurry when my browser zoom was at 200%. Content scale factor was not a variable here because it actually hadn't changed. It was still 1.0, but the browser itself was zoomed in.
After searching through Starling source I found that Painter hasn't yet implemented the "wantsBestResolution" boolean in _context.configureBackBuffer, so i added it myself. BOOM, 200% browser zoom and my textures are crisp and beautiful!
_context.configureBackBuffer(viewPort.width, viewPort.height, antiAlias, enableDepthAndStencil, contentScaleFactor != 1.0)
_context.configureBackBuffer(viewPort.width, viewPort.height, antiAlias, enableDepthAndStencil, contentScaleFactor != 1.0, true);
I suggest Starling gets a supportBrowserZoomFactor setting much like supportHighResolutions to make this a fully realized solution!