<spatialreference>102003</spatialreference>as comes in the eSearchWidget.xml by default it works great for me as far as getting a 3 mile buffer that measures 3 miles using the Draw or eDraw widget. Each projection has some distortion either shape, area, length so the WKID of 102003 is probably best for you unless you want to use the 1983 UTM WKID for your area.