Ice usually just means relatively pure meth
, because pure meth in crystal form looks like ice.
All of those methods produce methamphetamine
, but some (I forget which is which) produce more of the "good" isomer. There are two meth isomers (isomers are just molecules with the same chemical formula and connectivity, but with different geometries) one gets you high and the other not so much. I believe the "Birch Method" produces the highest proportion of the good isomer.
Regardless, all three methods produce methamphetamine and the purity depends on the technique of the chemist and the purity of the precursors. Often times when a batch is messed up somehow the impure end product can be further purified through various methods such as distillation and recrystallization, but some meth is lost every time you try to make it more pure so its best to get it right the first time.