Dealer support is good, but I don't think that's the clincher. Both of my local Stihl saw dealers are also Echo dealers. Actually, they both deal Husqvarna, too!
Right now, I own one Husqvarna, one Echo, and one Stihl (35, 51, and 85 cc, respectively). The Husqvarna is brand new, while Stihl and Echo are both older saws.
I can say that shopping for used parts and upgrades on ebay is much easier with Stihl than Echo, since there's just more of them out there. I also really dislike the chain brake design and gas/oil fillers on the echo, since they're on the top of the saw under the chain brake lever. Stihl has the nice LARGE tanks on the side of the saw, with filler necks big enough to fill directly from a 1 gallon jug without a funnel. Thankfully, Echo has also switched to the side-tank design on their newer saws.
Someone (MasterMech?) made a good comment about the two, when I asked a question similar to yours. I had pointed out that most landscapers around here consider Echo and Stihl brands to be neck-and-neck on most equipment, and he had replied Echo is as (or more?) reliable than any other brand, but they're not really known for pushing the envelope on performance.
One local dealer (he sells Echo, Stihl, and Husq) told me that Echo was a great name in chainsaws until the early 1990's, when they released their early "CS" series saws. Some landscapers had problems with these saws, and it soiled the Echo name. This dealer told me they've reworked their entire line-up in the last year or two, and he's very happy with their newer saws. He said he'd have no problem recommending a new Echo, right alongside Stihl or Husqvarna.
I recently bought a Husqvarna T435, because it had more impressive spec's than the similarly priced unit from Stihl. I didn't see that Echo had a whole line-up of top-handle saws (more than either Stihl or Husqvarna) until after I had already bought the T435, and now I'm having a little buyer's remorse, since those new Echo's actually look pretty nice! At the same time, I'm thinking of trading in my 510EVL for another Stihl in the 50 - 55 cc class.
Only bottom line is, you do seem to get what you pay for. All three makers have a range of quality, and prices to suit. You can buy a homeowner's saw, and farm/ranch saw, or a pro saw from any one of the three. That's the more critical factor than the brand name, in my opinion. A homeowner / occasional use saw from Stihl is not going to compare well to a pro saw from Echo, and vice versa.