for low paying niches image ads are always a blessing in disguise , otherwise text ads pay you a lot more but you should not try blocking image ads as they still help you boost up your income
I prefer using text ads instead of image ads. but mostly i use both and leave it to google, when to show text ads or image ads
i think image ads look better - customers will click them because they think with text ads 'Look, they cant afford an image ad'