Seemingly cold-hearted, but comparatively pleasant (5)
I believe the answer is:
nicer
'comparatively pleasant' is the definition.
('nice' is associated in meaning with 'pleasant')
'seemingly cold-hearted' is the wordplay.
'seemingly' becomes 'nice' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'cold' becomes 'dry' (synonyms).
'hearted' says to take the centre.
The centre of 'dry' is 'r'.
'nice'+'r'='NICER'
'but' acts as a link.
Can you help me to learn more?
(Other definitions for nicer that I've seen before include "More pleasant or agreeable" , "Even more 7 down!" , "More pleasant, French resort close to Montpellier" , "More pleasant or courteous" , "Kinder; finer" .)