For modelling, you have 3 choices:
I've done a lot of testing and have always used "every tick". I can understand the option to use open prices, if the strategy is based on that. But I honestly have no idea what the 3rd option (control points) can be used for.
So as a poster said, it doesn't reflect reality anyway, so do your testing with "every tick" and look for the best set-ups. Good and thorough testing take time. So conduct your testing scientifically and methodically and you will eventually get good results (if you system is good, of course
).
Happy trading,