Chainsaws are like boats, or guns. You may not need more than one, but having a quiver at your disposal is pretty nice based on application and intended use
If I had to pick one saw to do it all; drop trees, make firewood, prune, climb with, etc. it would be the Stihl 261 all day.
The power to weight ratio and versatility is the best in the Stihl lineup. Being one of the pro saws, it has the mag clutch cover and will generally be more durable with similarly sized saws. I find myself reaching for this saw more than the handful of others I have in the lineup.
Big production and big wood, the 500i is my go-to and it absolutely rips. Less power than the 6/800 saws, but much lighter and easier to wield. More than enough power for anyone for anyone but perhaps some production fellers working big wood. If you have it ported and put a Bark Box on it, it will keep up with any saw out there. Basically, can't bog it down. Kinda scary.
My first saw was the 290 and I still have it, but it rarely gets used falling between the 500i and 261 and being a homeowner saw with a lackluster power to weight ratio. I ported the exhaust which woke it up a bit, but still not as peppy as the 261.
I wind up using a 180C for limbing and groundwork and it is a great performer for the cost. Not a pro saw but surprising performance in an easy to handle package. If I was made of money the 201 would fill this niche.
For climbing I picked up a Stihl MSA161T battery saw and have had nothing but problems with it. The chain tension won't stay put, the thin kerf chain and skinny bar is super finicky about bar orientation, and it hangs up constantly, power to weight ratio sucks, heavier than gas counterparts with far less power. I will be replacing it with a Ripsaw ported Echo 2511T for a dedicated climbing saw.
If a pro saw is out of reach for price, there are lots of things you can do to the homeowner line of saws to get some more performance and life out of them. West Coast Saw makes some aftermarket air filters and ported exhaust products that can boost the performance of saw 8-10% for less than $100 for everything. Aftermarket dogs can make a big difference in making straight, efficient cuts. Eagan Saws is another source for performance upgrades for a wide range of saws.
The Stihl 2-in-1 file guides take most of the brainwork out of sharpening chains by addressing angle of attack and filing both the cutters and rakers/depth gauges.
Got wood?