Stihl or ECHO if gas. We had them at work on all sign maintenance trucks to trim branches for sight distance on signs. The other brands we had never lasted a year. It will have similar running issues as a string trimmer.

What I like is I don't have to worry about it starting. I run it from my Honda EU2000i (suitcase style) generator. It works for what I want to do. 

I've read that no one can find the correct replacement chain, but I will probably never wear out the original chain.

Same here, :) My Harbor freight saw works great but I find myself with either ALL my lead cords stretched out or my smaller generator on the cart behind the 616 :) I guess I need to either buy a battery powered pole saw OR rig up the AC generator intended to mount on AC garden tractors :)

I've used a bunch of different types, and my conclusion is that ANY pole saw is better than NO pole saw...

I've used the Stihl Combi type, and yes, they're heavy.  I used some generic asian import type that a friend bought, it had a 55cc engine... and while it was strong, I'm certain that if it was a Stihl, Echo, or Husky, it would have been TWICE as strong... meaning, at 55cc, it had a big-engine sound, but a 40cc Stihl was more powerful... so the asian generic was just not up to the performance-per-cc of name brands.

I've used electric pole saws on extension cords, and my favorite way to handle it, is with an extension cord on wind-up reel, on a small trailer with generator (and rack for tools) towed behind my zero-turn or garden tractor (IH Cub Cadet or Kubota)... by doing this, I don't need a whole lotta cord.  Typically, I'll have an electric chainsaw on a scabbard, too, for cutting up what falls.

Now, as suggested, yes, pole-saw chains tend to last longer than a usual chainsaw chain, and the reason is simple-  dirt is very abrasive, dulls chain saw blades instantly.  Trees accumulate dirt in each layer of bark... but MOST OF IT will be within 10-12 feet of the ground, simply because blowing dirt is usually not much higher than that (yeah, I know, dust storms, but in general...)...

So the pro's tip, will be that when cutting up a felled tree, use your little saw, with sharp blade, and start up at the top, and at the ends of the limbs, and work your way in, and down.  Eventually, when you get to trunk areas within 15ft of soil, you'll start wearing chains out faster, simply from the grit which has become encapsulated into the rings of the trunk.

One really handy thing about the pole saw, is that you can use it to knock lots of low foliage, particularly heavy stuff like vines and saplings, in areas that you'd otherwise have to crawl in on hands-and-knees to lop off.  With a pole saw, you can look in, poke it in there, and slice off a 4" sapling that's grown through the frame of an implement where you otherwise just couldn't reach.

Another thing you CAN do with a trimming saw, is make a 'comb' attachment where you can pass the chain bar through an area with lots of smaller things to cut... like... sculpting a runaway lilac hedge... without needing a ladder or long reach.

But a pole saw is not a replacement for having a general trimming-up saw, or a climber's limbing saw, or an arborist's pruning saw, or a timberman's big felling saw.

Looked at several brands. Visited with several knowledgeable people before I purchased an Echo gas extendable pole saw. That was 10 yrs ago. I have used it more than I thought I would & it's still running strong ~ good saw.  CAUTION:In a few minutes, it can deliver more cut tree limbs than I care to pick up/cleanup that day!! So my evolved thinking is; "when picking up the pole saw, immediately think cleanup, not trimming." 

DaveKamp is correct about less dirt higher up tree. I have never sharpened or replaced a chain. Chain is self oiling. Yes, you will need to adjust chain occasionally. 

Some other advice ~ always try to do a brief undercut on limb. That way as you cut limb from top downward, the limb will cut "clean" as saw moves to base of cut. Another words, undercut limbs (especially heavier ones) are less likely to "rip" a slab of trailing wood/bark downward from cut, possibly ruining the uncut limb's xylem/pholem in the ripped bark areas. What is a heavier limb? 4-8" diameter at cut. This also minimizes most blade pinching.