my awnser...both
I have to admit there are ups and downs to both. the micro is great for smaller batches (up to 2-3 cups) with no problems but the boiler is great for any thing larger.
the micro tends to scorch in larger batches, but the boiler evaporates the mostioure from small batches very quickly as well.
i tend to use what ever one seems easier for the amount of soap i am useing. its very easy to scorch larger batches in the micro because the already melted soap will insulate any unmelted, so you put it in again and again and before you realize it the soap is scorched, and it some times still has some unmelted soap!!! the reverse tends to happed in the boiler, while it is great for keeping the soap at a certian temprature it is also evaporating any mosture in the soap. this is fine for a larger batch as it takes a while for the majority of the mosture to disiapeare, but in a small amount 2-3 cups or less that stage will happen very quickly!
both methods will scorch, and both can evaporate the mosture out, so it is realy just down to which method would be most appropriate for the batch your working on at the time.