We've been going through this process as well. A big question to ask is do you want something that can be engineered and legally permitted by your county planning department? If your answer is "yes" that a lot of options get eliminated right off the bat in most cases.
My first choice was the Conelys 3Gen greenhouse, they are by far the most top of the line out there at the moment, but thanks to a curve ball the county building department threw at us in regards to the site prep, that greenhouse looks like it is no longer viable. Due to an absurdly massive and expensive retaining wall they wanted to see for the spot, we simply don't have the width and budget needed for it. Maybe for the next greenhouse.
Conelys does offer different, a smaller, cheaper unit with their Mountain 1300 series, whcih you might look again. They couldn't be engineered to the specs we need though, so for us they won't work. If you are interested Conelys can be purchased through Greenhouse Megastore out of Sacramento.
The farmtek light dep greenhouses could not be engineered to the specs we needed to be a legally permitted structure in our county, so they were out. Plus the smaller poly carbonate greenhouse I got from them a while back was the biggest POS I've ever seen (mostly due to manufacturing errors) , I don't have a lot of faith in their quality control.
Forever Flowering has been around a long time, and their greenhouses are pretty impressive when the work correctly, but every single person I've encountered who has dealt with them has had nothing but bad experiences, which makes me hesitant. Their greenhouses, just FYI are simply Agro tech greenhouses with a light dep retro-fit kit in them. You can buy the exact same greenhouse from Water Planet out of Arcata, but you will have figure out the light dep system on your own.
It is possible to do a retrofit light dep system with a model of your choice, but this also has issues. The automatic light dep systems are *very* finicky and difficult to get working right. The more you complicate the system, the more unlikely it is to work right. Truth be told I have yet to see a fully automatic light dep system that actually works correctly 100% of the time. Because of this whatever we end up purchasing *must* have a warranty as well as customer support, something you probably won't get with a retro fit kit.
At this point we are looking at Gro-Tech out of Rough and Ready. Their buildings meet the specs we need to comply with the county, they have in house engineers that can deal with any additional engineering and requirements from the county, and their prices seem reasonable. I am still waiting to hear back on a few specifics to make sure it will work for our site and do what we need it to do. Hopefully they will be the one since we already wasted 3 months prepping and planning for the Conelys 3Gen only to have it derailed at the last minute.
Honestly it's pretty damn hard to beat a simple PVC and wood set up with a golden arm or something similar. My old simple light dep hoop houses cost 10% to build compared to what we are looking at now, but of course they are a lot more work since you manually dep and cannot be heated efficiently so you are limited to fewer crops per year.