Well the SAIX servers are a joke, you get less lag playing on the EU servers...fortunately I have never had an issue with the ISgaming servers though so I just avoid SAIX at all costs. Better off not having servers like that at all if you ask me.
Just play on the EU servers, I have never played on the SA ones. I've also never had any problems playing internationally with HoN and any lag I may be getting is too small for me to notice.