Run everything and test test test
Agreed. You might be surprised by what works.
Though in general bigger ad blocks work better, especially in places where people's eyes end up or naturally move towards.
I also have often found success with a 728 x 15 horizontal link unit towards the top of a page.
I generally use the traditional blue links, 0000FF.
I also have tended to find blending the ads into the background of a page works better.
I have tended to find that text only ad units work better than image or text/image despite Google's suggestion that running both is better (though you definitely need to test this for your industry).
At the end of the day you need to try different things to see what works for your site and your industry (as ever industry is different and will have different ad inventories).