I use Telit/Sagem/Simcom GSM modules also as various GPS modules. After test U-Blox LEON G-200 + NEO-5Q i forgot all other modules. Quality more better.
http://akb77.com/g/gps/new-modules/ublox.png 
http://akb77.com/g/gps/new-modules/stm32-ublox.png
Right picture - GSM/GPS shield stay on top Arduino STM32 shield.