This is a quazzy energy question… but it comes up a bit, so…
So first, the principles. Underfloor heating and Radiators are “Heat Emitters”, which have the job of transferring the heat from the hot water, that was heated by your boiler, to the room. Rads systems generally operate using water systems at 55C. Under floor systems use water at 35C.
Radiators are cheap – Underfloor is expensive
Space they take up
Underfloor is out of site. Rads take up space, and some might even say are quite ugly.
Underfloor is fairly danger free. Rads are hot to touch, so might cause an accident
Heat up time – Response time
Rads can heat up a room quickly (since the water in them is hotter). With underfloor, it takes longer, so you need to have switched on the heating earlier to get the same effect (though being on for longer will not mean more cost, just longer at a lower setting)
Underfloor is better for keeping a background level of heat in the house. See thermal mass
Lower temperature water is more efficient, so underfloor
If badly controlled, underfloor heating can be waste lots of energy, so rads
Modern Condensing boilers (the most efficient boilers available), work better with lower temperature systems, so underfloor
If properly insulated, the walls, and floor are a similar heat loss, so nothing here
Underfloor allows you to put furniture wherever you want. With Rads, that can be a problem
Rads allow you to have any floor covering you want. With underfloor, heavy carpets are a problem
Some alternative technologies, such as Geothermal Heating only work with lower temperature systems.
I think it is likely that the lower temperature thing will become bigger and bigger in the future. The hotter you need to get the water, the more challenging. So in my dream house… underfloor
Underfloor doesn’t leak (if put in correctly day one)… something which can’t be tampered with by people… is usually less demanding on maintenance. In fact… rads are more likely to leak. (just don’t hammer a nail into the floor)
Underfloor won’t burn your feet
Retrofitting underfloor = money pit