volkdent,
It all depends upon how much heat (BTU's) you need. (How warm you want it in your Shop and how cold it gets outside)
And of course, how deep your pockets are...
The tube heaters (gas or electric) are the most expensive option for equipment, but have the least operating costs.
The unit heaters (the little ones hanging from the ceiling and sit in the corner) are a lot cheaper, but use more gas to heat the space.
Anything electric is the most economical for the equipment, but you pay a premium for the electricity.
I would talk it over with a furnace supplier / installer in your area. I'm sure they can provide you with a better recommendation that I can from the forums.
Doug
PS: When I re-poured my garage pad at my old house, I installed tubing in the floor to provide heat, but never got around to hooking it up... Oh well