I can't give you a 100% supported by research answer, but I have some insight

I think the best place to start is to ask Where else would they go

They couldn't stay in Europe, they would be recognized fairly quickly and the countries were was well established.

Northern Africa they would stick out some, the weather is rough, and it was heavily colonized by other European countries

Japan, again they would stick out like and the loss if WWII would put

American forces in the country

China - though it would be easier to hide from the allies they would stick out within the population. Furthermore the culture was so much different and the language and I don't think china allowed foreigners in easily

Middle East and India - largely comtrolled and colonized by the English and other European countries, they would stick out and the culture was very different

Sub Sahara - basically a death sentence

America - not and option

Australia - long trip and an English colony as well

South America - actually has some Germany ties, not big friends with many European nations, it was less established and more Wild West like, due to early colonization from the Spanish, Dutch and Portuguese it wasn't completely foreign . There were sympathizers , South America didn't get heavily involved in the war, the weather is fairly nice and it's not terribly difficult to get to or into. Perfect hiding place and really one of the few options they had.

I'm not 100% sure if this but I seem to remember reading that Germany had a small city or research hub. Something like that as well and it was going to be used as a staging point for American invasion or backdrop. Something to that extent but went largely un financed and as the war got bigger became a secondary concern. Maybe someone can confirm or shed light into that.