Although you can use Z-Waves devices with the system, Z-Wave devices cannot trigger alarms.
I prefer the PowerG detectors over the IQ detectors since the PowerG smoke detectors will automatically go off if the panel goes into a fire alarm and they have a much greater range. If you do decide to get the IQ Detectors, make sure you have the correct version of the IQ Panel. The Qolsys detectors run off of the 319.5 frequency which is used by Qolsys and Interlogix sensors. PowerG devices are supported on all versions of the IQ Panel 4.
Here are some helpful links about the sensors: