Well, I'll throw in on BEHALF of kero.
I have a Reddy 55k unit. I've had it since I moved to MI, 16+ years ago. It has needed virtually 0 maintanence ( I rinse out the foam air filter every season...big deal). I started out using twins to heat a pole building, and they worked well. The building was so drafty and tall, fumes were never a concern.
More recently, used with a thermostat, it's left on 24/7, and keeps my 3 car heated very nicely. There are fumes, no doubt, but not too bad.
And allow me to say one thing for them. I have NEVER gotten ANY kind of oily film on ANYTHING from using them. I have also NEVER had a problem with moisture. But my friend has a ventless propane, and it produces copious amount of water. So much so he HATE'S to use it. Go figure.
I would say if you are getting a film of unburnt kero, and excessive fumes, your unit is not providing proper combustion, and should be looked over by a service center. Clogged or partially clogged fuel pick-up, weak pump, wrong mixture, fouled spray nozel, mis-aligned plug, etc, can all lead to incomplete combustion.
Now that said, there are other, cleaner options. And if you can afford them, then by all means, go that route. But if a pair of these is what you can afford, I would not be too concerned with using them. I have recieved excellent service from mine, with 0% hassle. It all depends on what you can afford, and expect. Kero isn't my dream source of heat. When I get my new shop built (how many years have I been saying that?) it will have some form of forced air natural gas furface.
Oh, and I guess I'd go with 2 small rather than one large. If one goes out, you still have some heat with 2 smalls.