You can't really compare the two because Hogan is plastic and Gemini is metal.
Gemini is fairly new in the 1:200 scale, but their models have been quite popular since the beginning of production. I have two models from Gemini in 1:200 and they are both great.
Here are some pics of my Gemini Air Canada A321:
http://www.diecastaircraftforum.com/...nada-a321.html
I also have two Hogan models. Hogan doesn't have as much detail as Gemini, but they still have some great looking models.
You can find some pics of my Hogan Air Canada on this thread
http://www.diecastaircraftforum.com/...-300-pics.html
Manufacturers:
Plastic:
Hogan
Skymarks
Metal:
Gemini200
Phoenix200
Inflight200 (mostly retro planes and quite expensive, but worth the price)
Here are some inflight200 pics:
http://www.diecastaircraftforum.com/...flight200.html
http://www.diecastaircraftforum.com/...200-model.html
I'm also fairly new to 1:200 so I might not have covered all the manufcturers, but these are the most popular ones in my opinion