Well, I actually prefer stihl equipment most of the time. I personally think they look better and run well. This decision was pretty tough for me because of that. I like the way the stihl looks, and I love the gas cap (since they resdesigned it because of ethanal). I know a lot of people hate that gas cap but I like it. The 4 mix doesn't bother me a bit, as I have a stihl fs 110r. I have had it over a year and it still starts on the full pull most the time without even choking.
I also like how the echo looks, but I don't like the gas cap as much. It just feels cheaper, almost like the plastic is literally cheaper. It also ways a little bit more, but I don't think that will bother me too much. I'm not too tall, but I'm not a small guy either and can handle the weight.
It ended up coming down to the fact that the echo had a little more cfm, and many more positive reviews. The majority of people said you can tell the difference, although it wasn't much. The major deciding factor was the vent for your back, and the straps look a lot more full and comfortable. I figure the little extra weight would be offset by the better straps and the vent will be great.