The differences are highly technical and I'm not sure there is any clear cut "better" between the two. You can find tons of hype about micathermic heating if you Google the term, but actual studies or comparisons are hard to find.
Both technologies are fairly cool to the touch (unlike metal heating elements) and quite safe to use. And a btu is a btu , no matter how it is generated, so both heat an area about the same. Remember, there is no waste due to inefficiency in a heater - the "waste" is heat too.
I'd look for a heater that is quiet and has a thermostat that actually works well (most t-stats on small heaters are notoriously inconsistent, allowing wide swings in temperature at a given setting).
I am not familiar with one of the terms but I will make a statement about electric heaters here
All electric heaters are 100% efficent, ALL of them, there is not a single one that is 99% and of course 101 means you are getting more out than in (Though in theory a heat pump can deliver more heat per kilowatt, than a kilowatt can deliver)
So if someone tells you "This electric heater is more efficent than that one" they are lying
The reason for this is that ALL losses in an electrical or electronic system are expressed as heat, it's all heat, so even if the heater does not turn 100% of the enegery at the plug into heat at the element, it's still turning it into heat
I'll add to Gary information. With any portable heat source you buy be sure you have one that turns off if it gets knocked over. I was camping in an area a couple of years ago where if I ran out of propane it would be a big deal to get it refilled. I had unlimited source of electricy. The little cube ceramic heater we had worked extremly well. We have pets and I felt better knowing if one of them knocked over the heater it would shut off.