I pull these things apart as a bit hobby, so speaking from the inside of these things...
I'm basing all the below on your requirements in the OP.
Item 1: Bar length is based upon chain and cc's. The more aggressive the chain, the shorter the bar. For instance, either the Husq 455 or Stihl MS290 can pull a full chisel chain through hardwood on an 18" bar with no regrets. Increase the length to 20", however, and you'll get some bogging. Drop the chain down to a green safety chain, tho, and the MS290 will handle a 20" bar easy. For the homeowner, a green chain is best. Kickback is not to be triffled with. If you insist on the full chisel (yellow), buy a safety helmet. Seriously.
Item 2: CC's matter: homeowner vs pro, not so much. Both brands use fully lined cylinders, both have great quality. A Stihl MS290 and a Husqvarna 455 are both fully capable saws for what you're looking for. I've rebuilt both saws, have seen their insides and would rely on either brand. You DON'T need to spend the money on a pro Stihl like the MS260. Don't get me wrong, the pro saws are great, MS260 is four pounds lighter than the 290 for about the same power. But not worth the cost delta for a homeowner cutting a couple of chords of wood per year.
Item 3: Whatever brand you buy, take advantage of the premix fuel and the extended warranty offer that comes with it. Both brands will greatly increase the warranty if you buy their brand name premix. I'm a big fan, BTW, of the canned premix for light duty use. Yes, it's twice as expensive as mixing your own. Yes, you could use Opti with your own tank, but the premix has a FIVE YEAR shelf life! Great stuff and a good guard against future carb issues.
The gas thing is my favorite soapbox, so please allow me to elaborate. NEVER use ethanol gas in a small engine. (Lawnmower and up). If you're just gettting stuff out of the local pump, STOP! Find a station that sells pure gas and buy at least 89 octane. Put some Stabil in that tank, then pour into a smaller tank for your 2-cycle equipment. Don't use the crappy Poulan walmart 2-cycle premix, buy quality synthetic (Stihl and Husq gets longer warranty if you buy with the saw) The canned gas is great, no thought required, and keeps a LONG time. Great stuff for the homeowner.
There are three things that typically kill a chainsaw (or other 2-stroke):
(1) Running straight gas (no premix, too low premix) - easy to fix by buying canned gas
(2) Running ethanol gas which eats the gas lines and carb seals. Saw eventually develops an air leak, runs lean, scores piston/cylinder which reduces compression down to unusable.
(3) Shutting the saw down, leaving gas in it for extended time. Gas evaporates, leaves varnish and sludge in it's place. Some of those carb passages are a hair's diameter and clog completely up. Prevention is easy; when you're done, drain the tank, start the saw, idle till it dies. Then choke and crank until she won't fire again. THEN put it away. If you're putting it away for a month or more, pull the plug and squirt just a little fogging oil in there, crank a couple of times to spread it out and put the plug back in.
For (1) and (2), you have to replace the piston and cylinder. For (3), a carb rebuild kit will typically bring it back.