Your suggestions on Image VS text _image ads

for my site

[conjo_guam]

I have a 120 X 240 high paying text ads on my site at present.

Due to new additions and change in layout of my site, iam planning to replace that with
300 X 250 text_image add layout.
With my layout and content, i need image ads in 300 X 250 google add box. But, iam afraid of loosing money. I am not sure, if Image ads pay by impressions or by clicks or by both.

I tried using text_image ads, but i always see text ads there. This is because, Google tries to place high paying ads.

What should i do
1) Simply use Image ads and loose money? Not to mention, sometimes ads don't appear due to lack of advertisers.
2)Use text_image ads and loose little bit appeal of my site.?

thanks for your help.

[leadegroot]

Run a split test and see which works better.

[conjo_guam]

what is split test?

Use on and off both formats?

thanks

[leadegroot]

Try this:
[conversionchronicles.com...] (no affiliation)