We have three units: one older Panasonic, one newer Panasonic and a Toshiba. The Panasonic ones are better imho. They make less noise, build quality is better and emptying the water reservoir is also easier. The Toshiba works, but lacks the previous mentioned quality points of the Panasonic units. IOW, we will not buy Hitachi again.
They all work well up to 12m2, but for our living room we either use the A/C in dehumidifying mode or when it is cold we have a kerosene heater to keep it warm and dry at the same time. One 20 liter tin of kerosene will get us through a week.
We also have electric space heaters (the traditional ones), but the ones in Taiwan are usually underpowered (1200W max) due to the low current that 110V can deliver. For small rooms they are fine, but for bigger rooms you need two at least. I brought a 230V heater from Europe and feed that from the A/C outlet for my 18m2 study, but if you have a really big room kerosene heaters are the way to go.
BTW, stay away from the oil-filled radiator plate style heaters. They take forever to heat up and hardly produce radiated heat, so you will never get a room nice and warm. Apart from that they suck electricity like mad, so your bill will sky-rocket. We got rid of ours, so you know.