I have used IrfanView since seeing a link on ghisler page. Haven't tried anything else, except ACDSee which I uninstalled when trial ran out. IrfanView was better. I haven't tried Imagine, ImageLister, SGViewer, nor xnview. Are any of them better then IrfanView?
I tried Imagine just now and it is indeed very nice and fast! Will use it from now on. One feature though would be nice - Resample instead of resize when fitting big images to screen.