which is better? Stereo Amp or Monoblocks?

Yup, agree with Erik.  Monoblocks have completely separate power supplies, whereas most stereo amplifiers used a single shared power supply.  However, some stereo amps are described as "dual-mono", which are actually two amplifier channels with two completely separate power supplies and transformers (just mounted in the same case).  Some stereo amps have a pseudo dual-mono design where you still have a shared transformer, but the left/right power supplies use different secondary windings from that transformer.

Also, monoblocks are usually, but not always, a fully balanced/differential design (i.e. push/pull).  Some stereo amplifiers are balanced/differential, but 90% of the stuff out there is still single-ended.

Obviously, comparing a $500 monoblock with a $3000 stereo amp (say Rotel vs Parasound).  The Parasound is going to win.  I took this question to ask about amp topology.  Not which amp actually sounded better. 

Say you have a monoblock amp and a stereo amp with all the same component quality, driver circuit design, output devices, power supply capacitors, etc.  If the stereo amp uses a shared power supply, then the monoblock is going to sound better.  It may still sound better even if the monoblock is single ended.  If the monoblock is fully balanced/differentially, it will beat the stereo amp (as long as the it is properly designed for balanced topology -- some amp circuits do not bridge/mono well).