Any one of those should serve you very well, they are all high quality units. The C-4 is new technology and the long term reliability has yet to be established but it is likely the wave of the future. It is light and very clean. I'm still old school and would choose the Echo just because I like the light weight, power, and simplicity of two stroke.

Shindaiwa's C4 technology was introduced in 2001, like canguy said they haven't been around for decades like 2-strokes. But with proper maintenance, they should last a very long time. And they're definitely quieter than their 2-stroke counterparts. In fact, many people from just hearing them discard them as low-power machines, just because they're used to the noise of 2-strokes. But if you actually run them, you'll see that their tone is deceiving because they have lots of torque.

I have an Echo srm-200be straightshaft trimmer/brushcutter from 1984 that runs as good today as it did new. I also have an echo srm2400 string trimmer thats a little lighter and also runs great. I guess you could say that I have had good luck with Echo power tools. In addition, I have one of their pole saws and one of their big leaf blowers. I have continued to purchase their tools because they work for me without breaking down. They are well engineered, made in the USA and start easily. Not one of them have I ever had to take back to the shop. The only maintenance thats necessary is to replace the sparkplug, air and fuel filters every year and to drain the fuel mix out of them at the end of the season when your ready to put them away for the winter. I clean the carbon out of the engines exhaust ports every couple of years as I learned to do with the Lawnboys. Use a little extra two stroke oil in your fuel mix (32:1 rather than 50:1) and Im sure you will have the same success.
Good luck,
Bob.
Ps. I forgot to include that I have a pair of the Echo cs-520 chainsaws too.

To RMH 3481
Thanks for your info. I am surprise that your SRM 200 last that long. It is supposed to have only one compression ring!!
I have an Echo hedge trimmer and the only time I found it hard to start is when I forgot to turn the ON switch on!!!!. I don't get use to having an "on" switch!!! It happened too many times!!
You should respond to my latest posting about gas oil ratio since you use 32:1 ratio for many years and have no problems so other people can hear about this.

I have an Echo SRM210 that is two years old and has performed flawlessly. I highly recommend it. My neighbor has a 20 year old curved shaft Echo trimmer and he has had no issues with it.