Argon- and Air-filled IGU

Should I use an argon- or an air-filled IG unit?

Argon has a low thermal conductivity. Compared to air, argon gas filling improves the thermal insulation performance of insulating glass units significantly. The use of state-of-the-art manufacturing equipment and insulating glass sealants ensure the long lasting and gas density. Even breather tubes can be used in argon filled units for equalizing high-altitude conditions: