I am pretty sure this same topic just came up a couple of days ago. Search and Im sure you will find the thread.
I use both Stihl and Echo. Both are solid products but I personally perfer Echo. I have never tried RedMax or Shindaiwa because none of the dealers I have ever dealt with sell them. To be honest they are all solid and you probably cant go wrong no matter what you buy. If I had to choose between those three, I would pick the one being sold by the dealer you feel most comfortable with.
I have always used echo also.... not saying that the others aren't good or anything. I continue to use echo becasue it is easier to order parts for all of them from the same place, (air filters, spark plugs, blades, line etc..)