Keep in mind that Amazon is a big place, and your mileage can vary greatly depending on which team you are in. Personally, there are some good and bad points with my team (and pager duty always sucks), but overall I'm not discontent. I'm not sure about the pay-scale claims though. I had thought that I was being paid pretty well, and cross checking against external sites seemed to confirm that.

You can also just take the job at Amazon and switch to the MS offer if you get it and don't like what you see at Amazon. Its considered incredibly rude, yes, but our group has had that pulled on us a couple of times.