What do you feel is the best type of ads to purchase on other sites? I don't know whether to go for banner ads, skyscrapers or the square 125x125 kind.

I feel I notice the square ones more than I do banners. I'm not sure if that's because it's relatively new compared to how many years banner ads have been on the web or it's the positioning. Is that just me? Please share what kind catches your eye most.

What would be your preference if you were buying ad space and why? Thanks.