Hi DF --
I've only had extensive experience with my FLIR Thermosight RS32 1.25-5X, so I have no real comparison to other thermal sights.
However, I've peered through an Armasight 336 before, and the view looked pretty similar to my FLIR. Don't know much about its overall detection capability, effective range, resolution, etc. The sensor (known as a "photobolometer" in thermal jargon) used in the Armasight is made by FLIR Systems, so I suspect models from each company with equivalent sensor resolution and magnification will probably produce a similar image.
With that in mind, based on the reputation of the major brands (ATN, Armasight, FLIR Systems, etc) and comparing specs vs. price, I would say the overall best bang for the buck is probably the Armasight Predator 336 2-8X25 @ MSRP of $2795.00. This is probably the scope I would have bought had it not been for the fact a buddy had the FLIR RS32 for sale for $2300 (normal retail is $3800 - $4200).
The Sig Echo 1 thermal reflex sight has received overall good reviews, and it is less expensive, at "only" $2K. However, being a reflex sight with an "open" screen (think EOTech type form), it does produce some visible light that can give away your position, and it has lower resolution than the Armasight 336 and the entry level FLIR scopes.
Keep in mind that the things that affect the price are sensor size (higher the number of pixels of course provides better resolution), frame rate, base magnification (zoom on most, if not all is achieved digitally rather than optically), objective lens size, menu options, and brand.
For hunting, you really don't want a refresh rate less than 30Hz, with 60Hz being better. The higher the refresh frequency (number of times per second the image display refreshes), the less "jumpy" and blurred the view will be, which is especially critical for hunting moving animals.
In some ways, the Armasight 226 2-8X25 is superior to my FLIR 1.25-5X, because it has a bit better resolution at base magnification, since its base is 2X, and it has greater effective range. However, the tradeoffs are that it has narrower field of view and lower refresh rate -- 30Hz vs. 60Hz for the FLIR RS32. How much difference that really makes in real world hunting situations, I cannot say. But all things considered, 60Hz is superior to 30Hz. Since the zoom on these things is digital, increasing magnification also makes the image more pixellated, so zooming in has very little benefit to aiming precision or target identification.
I would say the FLIR RS32 1.25-5X I have ranks near the top in "best bang for the buck" since it is one of the lower priced 60Hz units. Still, it's a $1K jump up from the Armasight 336 2-8X25, so you pay a premium for the faster refresh rate.
In terms of resolution, if you expect to see the same level of detail you'd get from a conventional rifle scope, you'll be disappointed. Thermal optics have fairly low resolution compared to conventional "day" optics. Keep in mind, the image you see through a conventional optic is the result of reflected visible light, whereas a thermal optic "sees" heat differentials, producing a "heat map" of infrared heat radiation, and therefore, you don't get anywhere near the same level of detail. The power of a thermal optic is in its detection ability, not its resolution. Once you understand and accept the differences, you really begin to appreciate the remarkable capability of thermal. It makes any living being stand out in stark contrast with its surroundings, and unlike conventional night vision, it requires absolutely no light. In fact, the darker it is, the better it works. So, even though you don't have high resolution, you can detect living creatures much better through the thermal optic than you can any other type of optic, because of the heat differential between all living things and their environment. With thermal, critters have a hard time hiding from you, as you can easily see them behind foliage, grass, etc that you might not be able to see otherwise in daylight. Another great underrated benefit of thermal optics is if you have an animal down in the dark, it's much easier to find them than with a flashlight simply by scanning your surroundings and looking for heat. A warm animal stands out like a Christmas tree through a thermal optic.
In general, even though you can detect hogs and other critters up to 300-400 yds and sometimes further, your effective shot distance through a typical sub-$4K thermal sight is around 100 yards and under, maybe 150 yards in some conditions. This is due to resolution/pixellation and reticle subtension combined with low base magnification. This is fine by me, since I'm using my FLIR on a .300 Blackout rifle using subsonic ammo (for suppression), which has an effective range of not much more than 100 yds anyway.
I may eventually get a thermal monocular some day for scanning if the prices keep coming down. Right now, yes, I'm using my thermal scope for scanning. However, since hogs are seldom very quiet, I can usually hear them coming into effective range well before I target them in the scope, so I don't really need to scan a lot with the scope.
I hope this helps. This thermal thing has been a really fun journey for me!
