++ vs comprehension

[S.D.Mechveliani]

Which is better,   c []       = []
                   c (xs:xss) = xs++(c xss)
or
                   c' xss = [x | xs <- xss, x <- xs]
?
Which is likely to run more efficiently when composed with other 
functions?

Thank you in advance for your explanations.


------------------
Sergey Mechveliani
[EMAIL PROTECTED]