I have both of these saws
I have an Echo CS-4400 that I acquired (for free) from my mother in law shortly after I purchased a brand new MS 290 and between the two I prefer the Stihl MS 290. Below I've listed the pros/cons for each of the saws based on my personal usage:
Echo CS-4400:
Pros:
Fast chain speed
Lightweight (~10lbs incl. 18" bar/chain)
Uses standard Oregon bars/chains
Moderately easy to maintain (cleaning, sharpening), screwdriver required to remove the head/filter cover, standard screws throughout, nuts on side
Uses 50:1 gas/oil mixture, conveniently the same as my Stihl
Was free to me, otherwise would not have considered it
Starts reliably for me
Easier to physically control due to light weight and less power
Uses less fuel than the Stihl due to lower displacement
Plenty of power for what I cut for firewood (locust, walnut, oak + many other softer woods) but requires more time compared to the Stihl
Cons:
Less sustained power when cutting compared to MS 290 due to lower displacement
Chain tensioning screw is positioned parallel with a scrench making this task a handfull
Saw is old enough that it has little or no vibration dampening compared to the Stihl
Stihl MS 290
Pros:
Relatively fast chain speed on a 20" bar although I'll probably get a 16" or 18" to use most of the time in the future
Plenty of power to make it through long cuts faster
Truly easy to maintain - filter cover can be removed without tools, filter removed with screwdriver/scrench, nuts on side, Torx everywhere else though
Built in winterizing features (below 50 F), switchable using the scrench
Chain tensioning screw is positioned perpendicular to the bar in between the bar attachment bolts which makes it very easy to access and use
Plenty of power for 99% of my firewood cutting needs
Starts very reliably for me after it was broken in
Vibration dampening works very well
Cons:
50:1 gas/oil mixture - makes it a no-brainer to pick up the Stihl brand oil, pre-measured for one gallon of gas
Heavy (13lb (head only I think) + bar chain weight) compared to the Echo although I spend less time cutting with the Stihl so it probably evens things out a little
Must visit the Stihl dealer to obtain chains/bars. No on-line ordering that I'm aware of however a Stihl dealer happens to be less than 5 miles from my home
Harder to control due to heavier weight and more power
Uses more fuel than the Echo due to larger displacement
In conclusion, although the Echo is lighter, is easier to handle, and starts just as well, even for small jobs I prefer to use the Stihl. I get through faster and my hands still have feeling in them at the end of a longer cutting session. The vibration dampening in my new Stihl is so superior to the Echo that there is not a question as to which saw is more comfortable to use. Also I saw on Ebay that people are auctioning CS-440s (newer CS-4400 I believe) for well under $200. A new Stihl MS 290 should be around $350 which includes a chain and bar, a full tank of gas, and is assembled by a professional (those last two are required of Stihl Dealers.) A new CS-440 costs $300 at the Home Depot here and I believe some assembly is required. I use the MS 290 as my main saw and keep the CS-4400 as my backup saw (ever get your bar pinched?)
Side note - I had a chance to use a Stihl 064 with a 24" bar (pro saw, older version of a new 640) and not only did it have a very noticable increase in power over my 290 but it seemed as though it weighed as much as or less than my saw!