Whatever you do, do not use a h1 tag and then hide the text. This will damage rankings. While there is much discussion about it I decided to use text-indent to hide my text as a few reputable designers had recommended it.
Bad Idea. The next time it got crawled my ranking had been pushed from first place to the second page.
Well i think Headings tags are more reliable than image because the more heavy the image more time you site will take to upload. but it does not mean that you should not use image logo. Try some images that have lower space than jpg or tiff.