I agree with Jim, radiant is the best. The problem is the initial cost is much higher, but its worth it in the long run. I hate any type of forced air heating in a house, let alone a shop. In a house, forced air just stirs up dust and so forth, even in a clean house. In a shop, there's far more possibilities to have dust around. The forced air can make things a real pain.
I have a small electric heater with a fan on it in my shop right now. It works really well in terms of heating the shop (its only 13x21), but the fan causes issues with dust and I hate it.
Since you're going with a wood floor, you have the option of something like warmboard if you want it. Its not cheap, but its a great product. I've used it on several large additions and renovations over the last few years and its outstanding. There are cheaper ways to go than warmboard, but I just thought I'd throw it out there for you. The advatnage to warmboard, or some form of equivalent, is the response time is dramatically faster than in slab radiant heat. You can actually get away with turning off the heat when you're not using the shop and still be able to get the shop up to a comfortable temp in a reasonable amount of time. With an in the slab system, it takes a long time to raise the temps and turning it off isn't really advisable.
Good luck with everything. I'm really hoping to be able to do the same as you this year, but its still not a go for me yet.