and as for the thread's topic:
best? it's like what is the best steak?, best French fries? what is the best beer? etc. I like parts of all of the general comments mentioned here. of course, what is best for one firewood operation may not be the best ideal for another. the commercial firewood operation may be also a commercial arborist and runs his saws all day, every day. then again, there is the homeowner type cutting up firewood for personal use. and then again, there is the homeowner type who goes out into the bush and cuts and gathers lots of wood for firewood. nothing wrong with extra power, but is it the best? there are so many variables that can come into play to answer a question such as you are asking. for a lot of firewood cutting often a bigger saw can help speed up the job. I think 3 factors certainly could influence what is best for someone. a) intended plans for use (needs) b) saw weight c) budget.
speaking from 20 years of oak wood cutting and firewood making experience using mainly 2 saws... my Stihl 019T and my Stihl 026, I would say this. I probably have used my 019T more than my 026. i cut a lot of wood. the dealer referred to the 019T as a limb trimmer and the 026 as a workhorse. I have found that the 019T is a small dynamo of a saw. I often cut downed limbs up to 10-12" even bigger at times with it with ease. issue is how sharp do u keep the chain? that lil saw has constantly impressed me. so, with it being 46.5 cc and 2.5 hp (approx.) a mainline saw in this size will or could be best for certain types of mid range firewood work. depends on size of log and how long you will be operating it. (daily use, heavy, light or sporadic) I would not like to run it all day! but for a couple of hours or so making firewood chunks to split... it is great. I like Stihl so I would say depending upon budget and need... a saw of this size could be a best saw quite capable of mid range work. the 026 has been my 'go to' saw for larger trunks and limbs. it comes in at 48.7 cc with about 3.2 hp. I have used this saw for much of a day and found it to be comfortable to operate. with a sharp chain it will go to town! chain size would be important, too... I can run .325 or 3/8ths. it weighs 11 lbs or so... the gear you wear will matter too, imo.
to me how one sources the stock for firewood would matter too, and influence saw size. certainly type of wood would be a factor also. operator size would play an important role, also. and what you want out of a saw also comes into play for what is 'best'. for one guy, as an example, a 1/2 T pickup V6 suits him well. for another a 1T dually V-10 is the way to go. plans for use, capacity and budget all come into play for each to get the 'best'. full time firewood making for sale, or nice equipment to make firewood wood for home use? new or used? and I would want to also consider the type of splitter being used too. as to saws, there are 3-4 very good, popular brands out in the marketplace. each has their own following. for most firewood making as in getting down and doing some work, ie, making chips... and on a budget I would say 3.5 -5 hp 45 to 50 cc's. used and in good running condition usually means about 1/2 or so of new saw prices. if it starts and runs good, a quick look into the exhaust port will tell u a lot about how it has been used and cared for. in general, a carb kit install is simple to do, most used usually need one or could use one do to age of pulse fuel pump, metering valve, seats, etc. bigger budget, bigger guy... select accordingly.
well, in any event... no doubt whatever buy decision you make you will want it to be an informed one. hope this provides some information that at least for me has been time tested and may possibly be of help to you. let us know what you decide upon if your plans do suggest you buy a new chain saw. I wonder how helpful this thread will prove to be for you in the decision you finally make?