Personally I would stick to wired systems over wireless. My personal choice would be the Honeywell Galaxy dimension range above all.
However wireless systems have come a very long way, and if i was asked to install wireless system or a wireless system would be beneficial due to cabling issues, Like many people have already stated it would be the Scantronic I-on range hands down!
Scantronic have been producing radio accessories such as panic buttons and signalling kit on top of radio panels for a very long time, (and are pretty dam good at it) Also being a scantronic they are easy to use, simple to set up/commission and they just seem to last forever.
Regardless what wireless system you go for in then end, just ensure you replace the batteries when the manufacture recommends.