I-bonds are essentially 5-year TIPS with some side-benefits. Those benefits are tax deferral (not a huge benefit), tax-free if you use them for education, you can cash them out after 1-year with penalty, and you can keep them for up to 30 years. And in periods of deflation they pay 0% real rather than going negative as TIPS can.
TIPS are better for longer-term investments (>= 10 years) for the simple reason that they have a higher yield with longer-term offerings. I-bonds and 5-year TIPS yield about 1%, 10-year TIPS yield about 2%, and 20-year+ TIPS yield about 2.5% above inflation. TIPS also trade on the secondary market, so there's a possibility of making capital gains (and losses) that doesn't exist for i-bonds.