Those wick type kerosene heaters work very well if you keep them maintained, and they don't stink (very much...). My experience is with somewhat smaller ones, but they work all right usually. Pretty trouble free. They're very efficient, and burn reasonably clean once they're warmed up. One disadvantage is that there's no thermostatic control, and no real possibility for it.
However, not very fast acting. If you want something that will heat up a cold garage faster, the Master heater linked above, or a Reddy heater, etc. will get you warm in a hurry, which is good if you don't want to have to leave it on when you're not there. You can also easily hook up a thermostat to one of these, which makes it convenient if you want, for example, to maintain your garage at 40 degrees or so. That makes it really easy to bring it up to comfort level when you're working.
I use one of those heaters in my shop (about 1000 square feet, poorly insulated) and it works well. If the building isn't very tight, you don't have to worry much about fumes, but you need some ventilation, obviously. I can heat my space with a 50 thousand btu unit, but when my 50 burned out I replaced it with a 100K btu unit, which heats the area up quite fast. Of course, the space I'm heating is about 5 times what's proposed here, too.
The biggest disadvantage of the forced-air heaters is that they're noisy, and also you need a good bit of clear space in front of them for safety. If you like to listen to the radio when you work, forget it.
For a 10 x 20 garage, if it's not too drafty, I think the Dura Heat might well be sufficient, and reasonably comfortable and safe. It also has the virtue that you could use it in an emergency in the house without having to worry too much about noise and stink, and since it needs no electricity, it would be fully functional during a protracted power outage. The only problem I think you'll have is that it doesn't blow heat around the room, so it will have to run a while to get the whole area comfortable.
