cincystache's analysis above ignores any state income tax benefit to 529 contributions, which, if considered, can tilt the analysis in favor of 529s over ordinary taxable accounts.
I have three college age kids, and have saved for their college in a mix of 529s and ESAs. In my state, I get a state income tax deduction for the first $6,000 in annual contributions, which was effectively about a 7% gain at the time of the contribution.
I agree with the general consensus that you should prioritize your retirement savings over kids' college. In my case I knew I would not be willing to retire if I had not covered my kids' college costs, so I worried more about optimizing for taxes than I did strictly worrying about the ordering of retirement vs. college savings.
I will point out some things about the 529 that have worked out well for me:
1. I can easily move money between my three kids' 529 accounts with (essentially) zero tax consequences. My kids have taken time off from college to work, have switched schools, have gotten and lost scholarships, have gotten financial aid, and have just in general changed plans quite a bit. Being able to move money around as their plans change has been quite helpful.
2. If you use the funds for qualified expenses, there are zero taxes. And if you use the funds for non-qualified expenses, then only the portion used for non-qualified expenses is taxed, and even further, only the portion of those non-qualified expenses that were gains are taxed, and only then when you take the money out. Oh, plus a 10% penalty on those non-qualified earnings.
3. You can avoid the 10% penalty on the qualified earnings if your kid has gotten scholarships. All three of my kids have gotten enough in scholarships where I can avoid the 10% penalty on any non-qualified withdrawals.