I have done all 3 SDEs in Heston using Euler:
1. canonical
2. log(S)
3. explicit correlation in SDE
and I get the same answer! but not as good as QE. Still, the code I write is a good example of using C++ namespaces. and a good counterexample!!!
BTW I do not get NEGATIVE VALUES with Euler. What am I doing WRONG? Any more heston test data????