What wedrifid said. See also Rationality is Systematized Winning and the section of What Do We Mean By "Rationality"? about "Instrumental Rationality", which is generally what we mean here when we talk about actions being rational or irrational. If you want to get more money, than the instrumentally rational action is the epistemically rational answer to the question "What course of action will cause me to get the most money?".

If you accept the premises of Omega thought experiments, then the right answer is one-boxing, period. If you don't accept the premises, it doesn't make sense for you to be answering it one way or the other.