A good article on the basics of the conundrum:
http://www.pcmag.com/article2/0,2817,2407896,00.asp
The single thing that has me leaning toward GSM in this is the sim card = portability factor. CDMA usually requires the mobile phone company to accept and configure the device to their network.
How many places are you going where there isnt coverage? For trekking out in the wilderness?? Do you need 4G out in nowhere buttfuck, kansas?
Yes. Not because that is a destination, but because in the US we frequently drive city to city over sparsely populated areas. Also, ~20% of the US population lives in areas referenced as 'Rural'. Since 'Urban' is defined as population clusters of >= 2500 people, there are a lot of 'Urban' areas that do not get GSM signals.
On CDMA it is far easier to get a signal outside of cities (population >25,000), on highways, etc. Both CDMA and GSM cover major metropolitan areas fairly well.
However, that may all be trumped by one simple fact. Part of the GSM standard is to be able to pop a provider's SIM card into -ANY- GSM phone and have it work. CDMA requires on-device configuration.
Picture yourself with your brand new Pyra walking into a Sprint, Verizon or US Cellular store and having to beg the tech to input the secret codes to get your unapproved, and admittedly weird, device configured for their network.
Now picture yourself ordering a SIM card online from either AT&T or T-mobile to use with a 'bring your own device' plan. It arrives and you plug it in and turn on the Pyra - and you're connected. They never see what you're plugging it into.
If GSM had better coverage the choice would be easy. However painful, though - I'm actually leaning towards GSM as being the better option. That is mainly due to not having to plead with a provider to activate a device so I can pay them for the service.
These types of devices may be an interesting option to 'get more signal' into a home on the edge of GSM coverage:
https://support.t-mobile.com/docs/DOC-14947