To expand what has already been said. They certainly compete with one another for this purpose. IUL tends to be the better of the two choices when the outlay is large and the death benefit is of relatively little importance (you can generally get IUL to accumulate significant cash if the death benefit is set to the TAMRA or TEFRA/DEFRA minimum (you have to go with the higher of the two so as not to violate the other one). You'd then make use of the Guideline Premium Test.
If death benefit is a playing a crucial role in the planned design, it's tough to get IUL to look good cash and distribution wise against blended whole life.
Best bet is to look at both for all situations and go with the better looking of the two.
It's perhaps important to mention that risk profile is important. IUL is riskier than whole life (though not by much). For this there is higher potential reward. Whole life still wins the risk adjusted rate of return fight, but this doesn't mean it should be chosen for that reason.
