For the longest wireless range you'll want to consider a DECT headset that gives you 5-10x the range of Bluetooth headsets (30 feet vs about 300 feet).
A few most popular models to consider with the longest wireless range is:
Notes: results with any wireless headset varies on your work environment and how many barriers the wireless signal has to go through. For a more accurate expectation, any tech spec you read on wireless range, cut that in half.