which is better? Stereo Amp or Monoblocks?

+1 on stringreen being all over it.

+1 for stringreen.

The thing is you have to qualify any answers with 'all other things being equal'.

If you do that then monoblocks are the clear winner. One advantage is you can place them by the speakers and keep your speaker cables short. This can really help with definition and impact, particularly if you have 4 ohm speakers. But my speakers are 16 ohms and I find that short speaker cables help them out too.

Atmasphere,
What are the advantages of a loudspeaker system with a 16 ohm nominal rating???

I prefer separate monoblocks but each has its sonic merits.  After building both push-pull and SE amps, some of which have been very similar in design and build except one being monoblocks and the other a single-chassis stereo amp, I reached a tentative conclusion--- the main differences I could hear were actually in imaging and soundstage characteristics.  The stereo amp seems to have greater image density in the middle of the soundstage and less extension to the extreme sides.  The monoblocks have a bigger soundstage with greater extension on each side but images are not as precisely fixed in space in the middle.  Overall I prefer the monoblock presentation but I can see how someone else might prefer the stereo.  I say "tentative" because it is really difficult to be sure what you are hearing is due to the monoblock vs. stereo chassis and not some other issue, but that's what I have heard on a couple occasions when I was able to make such a comparison.

@ mr_m

What are the advantages of a loudspeaker system with a 16 ohm nominal rating???

All amps have less distortion driving 16 ohms as opposed to 8 or 4. Tube amps in particular will not only have less distortion, but (if transformer-coupled) will play with wider bandwidth and slightly more power because the output transformer is more efficient. 

With our amps (which have no output transformer), there is less heat and power draw from the wall; the smaller amps we make (M-60 and S-30) also make more power.

Finally, the speaker cables have far less impact on the sound and you can run them longer lengths.