Not sure. Neither one would be really motivated to kill the other so that would be a factor. Jason can always come back but he does die a lot. Myers isn't immortal but he's damn strong and has only died once in the series (Unless you count Resurrection which was just stupid in my mind)
They seem pretty evenly matched in my mind but Jason seems to have more shortcomings and i've always like Myers better so i'd probably go with him.
__________________
|