well actually i would say Delphi because you NEVER hear about someone who just wrote a Delphi trainer. It's just not so common. Wait now that i think about it, Cheat engine was written in Delphi and all of the anti cheat companies must have LOADS of ways to block pascal made trainers...
ASM seems to be a trick question because it seems undetectable since a program is not very likely to find changes in It's OWN CODE... but then again you do need to have some sort of program that would inject the code, most likely written in Delphi or C++, thus proving my previous point.