Text does way better. The reason for me is that there are 3-4 ads in one block, so the user has a greater choice and a higher chance of a better targeted ad.
text ads get me 8% CTR image ads get me like 1% CTR, therefore I use text ads =) whats hard to convert are google referals!!!
Text ads have outperformed image ads for me so far. But Image ads, somehow seem to have a better CTR. All in all, so far, both of them have been equal in terms of earning. It might also be, because of the niche I'm in. I've tested it in entertainment niche so far. Should thoroughly test in the other niches, before I conclude on anything. Anyone else tried image ads in niche out of entertainment/games/music ? ~G
On my text based sites, I choose text ads. On my image based sites, I choose image ads. On my forum sites, I choose image ads.