That depends on how long you’re willing to tie up the money. Rates on I-bonds change again in May. But if you purchase now, you get the current 6.89% rate for 6 months, before the new rate kicks in.
Like T-bills the yields will change depending on the current level of interest rates and fears of future inflation.
You can buy a maximum of $10,000 in I-bonds in one year, but there is no limit on T-bills. Minimum is $100.
Read this: https://www.terrysavage.com/t-bills-beat-cds/
Maybe do some of both?