I never had good results with a 160x600 ad block placed on the right. I haven't tried it on the left, but I have a feeling, it will work better since people have the tendency to look at the left. How many of you are using a 160x600 block on the left and having good results?
I've placed ad on right, since on the left it's main content which will disturb readers. Otherwise it depend how does you site looks like - can you provide us link to your site?