I was leaning more towards the regular NG hot air heater type. Radiant would be nice, but i'll be moving all about the garage and not sittin in any one place.
Have your HVAC guy price a ceiling mounted gas fired unit heater. Put it in the corner opposite your biggest door. They're not too noisy and the new ones are 95 to 97% efficient. That small of an area would be easy and economical to heat after you insulate the ceiling.
