192T = lightweight, you can buy one new for less than $350, the climbers take it up the tree if we are trimming/pruning, it is light enough for a full day hanging from your hip.
192c or 192ce = a rear handle version of the 192T, goes for a few dollars more than a 192t used, out of production I think, lightest pro rear handle ever made by Stihl, homeowners tend to abuse a small rear handle so maybe a better choice for next to the chipper for pros, rather than homeowners. The different leverage of a rear handle makes folks think the 192ce is weaker than a 192t but in reality it cuts smoother and faster if you don't lay your weight on it.
020T = older version of 200T, differences are cosmetic, unless you have a preference for flippy caps (200t) or screw on caps (020T), can be had used for about $50 less than 200T
200 = just like the 200t, though a bit scarce in the marketplace, it is a small rear handle with very nice power, a good choice for a homeowner wanting to limb up around the house, pricing about the same or a few dollars more than the 200T
200t = pretty much the gold standard of top handle pro saws, there may be contenders amongst other brands, but check a pro truck and see which saw the workers get to work early to "claim" for the day, PRO TIP: it's a 200t. in nice shape they are worth $450 to $575, lots of nice rebuilt saws out there
201t - new model that replaced the 200T, go for a bit more new than a 200T used, but that extra $ gets you a warranty and dealer support for whatever that is worth in your area. The last guy to work on the arborist crew has to settle for the 201T, but in all fairness, if you don't mind kicking in an extra $250 and voiding your warranty, there are number of fine gentleman who can turn a 201T into a 200 killer, again probably not the best choice for a non-climbing homeowner.
150t - personal use limited to about 5 mins at dealer, it is lighter than a 192t and feels really nice in the hand. When we start up arborist operations in March, I will let the climbers decide if we should buy them to replace the 192s, the 150t is about $150 more than a 192t
020AV - this is a solid-ass saw, but I am not ever going to run one, too heavy and just feels clunky to me just standing on the ground with it in my hand I have no desire to fire it up, pretty darn cheap, have a few in a box in the shop, the old school Stihl logos on the recol are worth more than the saw itself to me
With the exception of the 150t I have all of these in my shop now and have used them all as well as having climbers who have used them all.
Dave