As mentioned - you can transfer beneficiaries if you need to. Also - 529's belong to the owner (parent or grandparent) not the kid... Which can help with financial aid by FAFSA rules. In fact, if it's owned by grandparents - it doesn't even show on the FAFSA applications. I think (but am not sure) UTMAs are owned by the kid -so they can hurt any financial aid. FAFSA considers assets owned by the kid 100% available to pay for college.
Yes, you can change the beneficiary - generally to a pretty broad variety of relatives (siblings, cousins, parents, etc.).
529 assets are the child's but 529 accounts also have a custodian - usually the parent or grandparent. For FAFSA purposes, 529s with the parent or student as the custodian are treated as parental assets and thus are "FAFSA taxed" at a lower rate than student assets.
While grandparent 529s (or aunt/uncle 529s) are not reported on the FAFSA, any 529 distributions from those accounts I believe are counted as untaxed income to the student in the year of distribution, which is "FAFSA taxed" at 50% for that year (which is two years later nowadays, so a grandparent 529 distribution in 2020 would affect FAFSA aid applied for in October 2021 for the 2022/23 school year.
UTMAs are student assets, and while they are 100% available to pay for college like any student asset, they are only "FAFSA taxed" at a rate of 20%.
Do note that some schools use CSS Profile for their school-granted financial aid. CSS Profile rules are different from FAFSA rules.
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OP, I'd look at a few factors:
1. Do you want your gifting to be intended for college?
2. Do you think (at least some of) your grandkids will go to college?
3. Are your state tax deductions for 529 contributions valuable to you?
The more you lean towards "Yes" on these three questions, I'd lean towards a 529. The more you lean towards "No" on these three questions, I'd lean towards a UTMA.