In my case I wanted to have a logo / image centered instead of a text. In this case, centerTitle is not enough (not sure why, I have an svg file, maybe that's the reason... ), so for example, this:

appBar: AppBar(centerTitle: true, title: AppImages.logoSvg)

will not really center the image (plus the image can be too big, etc.). What works well for me is a code like this:

appBar: AppBar(centerTitle: true,
    title: ConstrainedBox(
        constraints: BoxConstraints(maxHeight: 35, maxWidth: 200),
        child: AppImages.logoSvg)),