High Reliability GSM/GPRS Modem

[RoadRunner]

i am currently designing a bit critical communication system, in which we have multiple mediums of communication like GSM , VHF radio.  and currently i am looking for a highly reliable GSM modem to be used in this system.  for now i am thinking of Moxa , visiontek , u-blox GSM modules. 

so my question is if you are in the position to chose a high reliability GSM modem then which would you chose? any suggestion?

please help

thank you