I have a 35 or 45 thousand btu reddy heater in my single car unisulated garage I run it on diesel fuel for the most part mainly because a gallon of diesel rings in around 4-5 dollars and a gallon of kerosene is up near 15 dollars a gallon

The heater heats up the space in about 15 minutes and it will stay comforatable for a couple hours unless you are opening the door all the time. The main difference between kerosene and diesel is the odor when starting up and the warm up time of the heater you get more fumes with the diesel on startup and it takes a bit longer to get the heater running at it's peak after they are warmed up there is not much of a difference between the two.
I use the heater to get the garage up to temp then turn on the baseboard heater to maintain the temp and keep the noise down You may also want to look into the vented heaters if you are alloud to put them up in you're condo's garage they are quieter and they produce no fumes I would vote for kero or diesel over the propane model it is much easy'er to keep supplyed and you can go down to the gas station and get a gallon at anytime vs having to keep the propane tank full haul it around to the filling station and pay 20 bucks for them to fill it