This question comes up a lot and I've been asked more times than I can remember which type of goggle is better. We've owned both with most of our time with articulating goggles, about 3 years, compared to a little more than 5 months with fixed goggles as of this post.
The articulating goggle we had is the NVD-BNVD-SG (Night Vision Devices Binocular Night Vision Device, Single Gain Control) and the fixed goggles are the Adams Industries Sentinel and Anvis-9 aviator goggle.
There are other articulating goggles besides the BNVD-SG, such as the ACTinBlack DTNVG, FLIR BNVD 51/40, PVS-15, and PVS-31. There are several differences between them that I won't get into. The main thing is that they all articulate. I'll mention that the PVS-31 and FLIR BNVD 51/40 have interpupillary distance (IP) stops in addition to rotating monoculars (pods). This means it's faster/easier to get them back to your eye spacing distance. Some guys have used zip ties to do the same thing. I've never tried it.
Likewise, there are other fixed goggles such as the RNVG and Mod-3. Same thing, I won't get into the differences. They have IP adjustment like the Sentinel and Anvis-9. You adjust knobs on the side of each pod to move them in/out for your eye spacing and they stay in place once set.
I also won't go into other details like battery packs or the type of tubes (gain or no gain) for the different types of housings. The main thing people want to know are the pros and cons of the two different types of goggles and if one is better than the other.
They both basically work the same when they're down in the deployed position and you are using them. What really matters is the quality of the tubes inside. They do all the magic.
I personally feel an articulating goggle is a better overall choice than a fixed one because you have more options for how to wear and use them:
1. Deployed down both eyes being used.
2. Use as monocular with dominant eye. Weak eye pod up.
3. Use as monocular with weak eye. Dominant eye pod up.
4. Use unaided eyeballs with both pods rotated up to eyebrow line.
5. Stow the goggle with pods rotated out so it lays flat on the helmet.
6. Stow the goggle just like a fixed goggle.
Compared to just two for a fixed goggle:
1. Deployed down using both eyes
2. Stowed up on helmet not in use
Here are some things that might help you decide which might be best for you.
#1. Price. Articulating goggle housings cost more than fixed goggle housings.
#2. Simplicity of use. Fixed goggles are quicker and faster to use when seconds count. They stay in the correct eye spacing position (unless your helmet shifts significantly) and will be in the same spot when you go from deployed to stowed and back to deployed. The pods have the potential to move out of place with an articulating goggle and you might have to readjust them to get them back in line with your eyes.
#3. Vehicle use. Articulating is better if you'll be in/out of vehicles wearing your goggles and not always nods down. Rotating the pods up to your eyebrow line versus stowing them reduces the chances of smacking them on the ceiling or door frame. It's not just to avoid damage to the goggle but to your neck. It's a serious consideration if you have neck problems. Articulating doesn't matter if you're driving under nods but it can matter when you need to go nods off.
Example: I would often drive to a certain spot putting my BNVD's on before I left pavement with pods rotated to my eyebrows turned off. This way, when I got off pavement I could quickly turn them on and rotate them to my eyes. I never had issues moving in/out or inside of vehicles wearing them this way. When I first drove with the Sentinel (obviously having to stow them while on pavement) I had to stop and get out for something. I smacked the goggles hard torquing my neck on the way out. It hurt. I've done this at least a few more times off of vehicle ceilings, door frames, etc. whereas I'd never done that with the BNVD's. It took some getting used to.
#4. Extended use. Articulating goggles will be more comfortable if you'll be wearing them for extended periods without being able to remove your helmet. You can stow the goggle on your helmet and rotate the pods flat, moving the weight closer to your head versus having the goggle sticking out front wearing out your neck. It's not a big deal for short periods but you'll feel it after all night long.
#5. Weapon sights. This is a wash in my opinion. If you'll be using a thermal or night vision scope while wearing your goggles, in my experience you'll have to stow your goggles regardless if they articulate or not. Rotating the pod on your shooting eye may not clear your scope and you might have to contort your neck to see the scope. It's easier, faster, and more comfortable to just stow it.
#6. Durability. Articulating goggles are technically less durable than fixed goggles due to the hinges that allow the pods to articulate. They are not easily damaged and it would take a significant impact to break them at the hinge. Keep in mind that every goggle's weak point is the interface between the pods containing the tubes and the bridge that they attach to. They all have the potential to fail in that area however the most fragile parts of any goggle are the optics and the tube itself. If the impact is hard enough such as dropping it from a significant height onto hard surface, it won't matter how strong the goggle housing is if the tubes can't survive. I consider the durability to be a wash, other than the RNVG, which is the most durable goggle available at this time being constructed from aluminum vs a polymer material.
Hopefully this info helps you out. After using both types of goggles, I'd take either one depending on the circumstances, such as price and what tubes are in them.
It's pretty clear that articulating goggles have taken over as the primary type of housing in the military. This is evidenced by the widespread use of the PVS-31 and the new fused ENVG-B goggle. Both of them articulate.