Why do people require a larger pieces for flower and a smaller piece for wax?

This is a misconception in the industry.  It used to be that people wanted big hits, the larger the pipe, the bigger the hit they think.  Back in the day there were no concentrates.

Today much of the glass is made by kids with small arms so they can not hold the larger glass.   They claim it helps deliver better flavor, we find it is because they need more muscles.

What is the best butane for extraction?

We do not recommend that anyone extracts cannabis at home with butane.

But is there a difference?  Mostly it does not matter, the fact is that it needs to let sit anyways to let the butane evaporate.  If you do not want to take chances with butane, look into raw dabs (vaporizing flower) with a Silver Surfer vaporizer.