Which is better for SEO: text hyperlinks or graphical hyperlinks?
text hyper link
I have seen about.com and few other top sites use the image hyperlink because they want more pageviews. I guess it also helps from the SEO side.
text hyperlinks are better than the visual hyper links ..because robots always catch text links
Firstly, for anyone else reading this: a graphical hyperlink is where a link on one web-page which will take you to another is provided as an image rather than text.
The HTML image tag can include two descriptive text items commonly called the ALT tag and TEXT tag (text tag is not image specific but is often applied to images).
The ALT tag is intended for people who can't see the image. 15+ years ago internet connections were unbelievably slow compared to today and users could instruct web browsers not to download images, otherwise image-rich pages could take minutes to load. The ALT tag would help them decide whether or not to fetch the image. Now the ALT tag is mostly relevant to blind users.
The TEXT tag is better used for additional descriptive information. Just how that is used depends on Browser software but the most sensible is that the text is displayed when the mouse pointer hovers over the image (some browsers may do the same but show the ALT text instead).
So to give a practical example: suppose you had a photo of a blacksmith's anvil, the ALT text should just describe the photo. Something like "A blacksmith's anvil marked with a picture of a mouse". The TEXT tag might then give more description like "Anvils are used by blacksmiths for forging heated iron into shaped products (e.g. horseshoes). The Mouse is the trade mark of Mousehole forge in Sheffield, anvil manufacturers since about 1780".
The primary consideration for any text on a web page is its value to human readers, however webmasters seeking to get better search results from such as Google can attempt to do so by judicious choice of textual content. This is SEO (Search engine optimisation).
Exactly how Google works is their best kept trade secret and they constantly change their formulae to prevent people "gaming the system" for undeserved advantage. That means any question about "how to do SEO" can never get a definitive answer, the best is what Google themselves say in their Webmaster Guidelines http://support.google.com/webmasters/bin/answer.py?hl=en&answer=35769
You should also take note that Google will downgrade your web site or even drop it entirely if you appear to be using certain techniques to try to fool them into giving you better ranking.
"Higher Google ranking" is a meaningless concept unless you specify for what search phrase. If you have a page about the history of anvil manufacture then your aim will be to get good results for the search "history of anvil manufacture" but if you were to search for just "anvil" - well try it, I just did and got 26 million very diverse results. Trying to optimise an "anvil history" website for that single word would be near impossible.
A text link might just be a single word like "more" (and styled to make it clear that it is a link) but is better if it is descriptive like "history of anvil manufacture" because Google will "read" that text and will probably rate the page higher for "anvil history" related searches.
Even better, if the page the link goes to is called something like anvil-history.html (and with an image link, if the name of the image file is say mousehole-anvil.jpg that will probably help too especially in image search).
So to answer your question the best possible combination is:
Image link with an informative adjacent text link
Thoughtfully constructed ALT and TEXT tags.
Suitably named image file and destination page.
Destination page Title and Description tags also contain the relevant key words.
Destination page does actually address the topic, you're not trying to trick people to go somewhere completely irrelevant. (Think here about heading tags and body text).
A well constructed image link might be expected to do well in Google Image search too.
In that case the answer is "graphical links are best".
To do all that for every image on a web site demands more time and effort than most are willing to spend. In that case an image link doesn't have good ALT, TEXT, adjacent text link, image name and destination link then a text link is better.