It varies by company and changes from time to time, but 26" to 30" is common.
I am not a fan of miflex hoses as they are too torsionally rigid and that usually ends up in less than clean hose routing.
My preference is a long hose - 5' for recreational diving in a conventional jacket BC with no waist band to tuck any excess in - that runs down the right side from the regulator, goes under the right arm, comes up across the chest over the left shoulder and around the back of the neck to your mouth. It lies flat against you and won't extend out over a shoulder, snag anything, create excess drag, etc. And in an OOA situation the OOA diver can take your primary reg and breathe in comfort with enough slack in the hose to allow a normal ascent, safety stop, etc.
Alternatively, I'll go with a very short hose - just long enough to go from the first stage to the second stage with enough length to let me turn my head all the way to the left. In both cases I prefer to use a fixed, one piece non swiveling 90 degree or 120 degree elbow to keep it closer to my neck and reduce the hose length required.