Updated 2nd October 2018
Radiators as a heat source have had their day - underfloor does a much better job at keeping your house cosy, looking stylish and environmentally friendly.
If you don't like walking on cold tiles, if you don't like your wall space cluttered by ugly radiators, if you don't like draughts and want your house to be cosy warm throughout then underfloor heating is the way to go.
Radiators are often chosen because they get hot fast when working off your favourite fossil fuels. However all the hot air the radiator generates rises straight up your wall to the ceiling where it will tend to sit. All that lovely warmth will be hanging over your head and unless you live in upside-down world you don't benefit from the tropical temperatures that will build up on your ceiling. Eventually the room will heat from the top down with your head receiving the most heat (giving you an unpleasant stuffy sensation) and your feet the least. You can forget about kitchen and bathroom tiles ever getting warm and you should instead invest in a nice pair of comfy slippers for yourself. You can enjoy a daily game of "slippers hide and seek". Or if you find it hard to wake up in the morning put your bare feet on the cold tiles to give your brain an icy jolt. The first thing you will think is 'why didn't I get underfloor heating!'. Of course if you are a slippers fan you can still enjoy them on underfloor heating - they just don't need to lined with polar bear fleece to keep your toes toasty.
As the radiator drives warm air up to your ceiling it draws in cool air from the floor. And what's another word for air movement - yes that's right - a draught. And draughts are famous for one thing - making you feel cool. Radiators work by creating a continuous draught - so at the same time it is warming up the air it is also giving you a wind-chill - talk about giving with one hand and taking away with the other.
With underheated feet and a overheated head along with a continous draught you can forget about feeling cosy. If only there was a system where a gentle warmth was generated directly beneath you and warmed your feet equally to the rest of your body. Well, you guessed it, there is - underfloor heating!
So in summary radiators are bad at heating rooms and look terrible! If I had the choice between radiators versus underfloor heating I would definitely give underfloor heating a try. Unfortunately I have decades of non-cosy heating ahead of me and a houseful of ugly radiators to look at. Underfloor will cost more to install than radiators but you will get a lot more value for money.