Underfloor Heating
Pros
Underfloor heating operates at a lower temperature than a radiator-based system, making it more efficient
As underfloor heating does not need high water temperatures to operate, it is particularly well suited to heat pumps
Underfloor heating frees up wall space, giving greater flexibility with the placement of furniture and the interior design
It distributes an even heat throughout the room/space, meaning no cold spots - creating a comfortable living environment
Cons
It is not as instantaneous as radiators (depending on the set up); although, conversely, radiators also cool down faster
The floor finish needs some consideration
An underfloor heating system arguably requires more planning and needs to be properly installed to ensure it runs at optimum efficiency
Radiators
Pros
Radiators are quick to respond to desired changes in room temperature
Radiators are a familiar option and well understood by almost all heating engineers and plumbers
They are typically cheaper to buy and install
Can offer a place to hang towels etc in bathrooms
Radiators are comparatively less disruptive to install in existing homes with radiator-based systems
Work well with an existing boiler
Cons
Radiators do not distribute an even heat throughout the room, which can result in cool spots
They cool down quicker than underfloor heating
They are less efficient
They take up wall space, which can provide less scope for window/door placement and furniture layout
Cheap radiators can distract from the aesthetic of a room. That said, "designer" radiators may complement the overall interior design scheme