Hello Newt. Those are both great aircraft. As I think you know, we supply a lot of commercial aircraft for a very wide range of uses including the ones you have identified above.
One very significant piece of input on your side will be the sensors you need to carry around the power lines and cell towers. In many power line inspections, you may be taking RGB and IR images. We were part of a large effort with our local power company for this exact mission. The pilots flew M210s with X5S and XT sensors. 1 flight, 2 simultaneous sensor captures.
We have another client now that is highly interested in corona sensors for an M210. This is a more advanced power line sensor and after speaking to a manufacturer about the sensors, they will not put them on a 4 rotor system due to the weight and cost (too much risk).
Power companies are also using LIDAR. Lidar solutions of varying scales can use both the M210 and the M600.
As for cell towers, we do a lot of them. Basic photogrammetry inspections can be done with something as small as a Mavic 2 or Phantom 4 Pro. Advanced inspections (such as a contract we are working on now) might require thread counting on small components on the tower. The one we are working on requires a z30. While a Z30 can fly on either platform, flying near towers might be easier with the smaller copter.
Batteries are also a consideration - although not the most important one. The M600 needs 6 to fly for about the same time an M210 can fly with a pair of TB55s.
Other items to consider might be size and ability to travel, technology, obstacle avoidance, redundancy, RTK system (if you feel you need one), wind performance, sensor integration, etc.
The M600 has always been our favorite to fly, but unless you have some special or heavy sensors to fly, the M210 if a solid choice.
Finally, if you decide to move away from DJI sensors and look at some of the Payload SDKs, you may even be able to consider something like an M200.
We do not advertise this, but we are holding some original M200s and an M210 in stock and have dealer demos of both available if you want to start at a lower price point.
I you would like to chat offline about pricing and options, give us a call or we can call you.
Thanks!
Michael