Class D seems perfect for subs, since there's lots of low fequency power available in a cool running package, but I understand these modules can be complex and more costly than modern implementations of classic AB style circuits, which can now be made with no crossover distortion (if there is, it's well into the very low noise floor).
Just 'cos it's the latest thing, please don't automatically assume it's "better," since that's why GOOD valve designs can still offer so much pleasure. People like Quad (77 and 99 series) and AVI in the past have made some truly excellent Class AB designs which can sound sweet toned (Quad) and clean with excellent dynamics (AVI). The circuits have been fairly simple too from memory if the transistors are well chosen but I do admit it's a few years since I looked inside one of these...
Tear down these walls; Cut the ties that held me
Crying out at the top of my voice; Tell me now if you can hear me