A. If your state offers state income tax incentives for 529 plan participants, you should always participate because that already guarantees you a certain return.
What if your state offers no income tax deduction for 529 savings?
Now it's time to do some comparisons - if you believe your capital gain in the 529 savings will be average 6% per year, and your average long term capital gain tax rate is 25%, then the capital gain tax saving associated with 529 plan will be 1.5% (=6%*25%), if your 529 plan funds' fees exceed 1.5%, it's a signal 529 plan is not a good option for you. But you can always shop around to use another state's 529 plans, such as Utah or New York states' 529 plans which are known for low fees.