unless your garage is insulated, neither one will be efficient over time.
my garage is insulated and last night the temp w/out heat was 40. i run a small portable propane one http://compare.ebay.com/like/120446652334
it keeps my garage (725 sqft) at a warm 55. with the insulation, 2) 52" ceiling fans and this heater going, 55 is t-shirt warm. i keep east and west garage door's opened up approx 1" and crack the sliding window the same, for oxygen replenishment. My heater is kept on the low setting and it does the job.
Kerosene smells, even using the odor free, cost more in the long run, and does not work for my needs. I have a 40lb bottle of propane and that usually last me all winter long.
your heating investment should be decided by how much you use the garage.
are you in there using it as a business, or just hobby, the usual working scenario? if in there 6+hrs a day then invest in an overhead propane or NG system. If you have a detached garage like mine (100' from the house) then consider a 100lb tank for your supply. I can't as i would have to trench NG line across the sewer line, with or w/out a permit it is a no go here.
try throwing used carpet or those 3x3 work mats on the floor. warm feet is 1/2 the battle.

ALSO make sure you have something to ground yourself to before handling powder