I bonds appear to be a poor man's TIPS (Treasury Inflation Protected Securities). Right now they pay interest at the inflation rate plus - zero. Yes, the underlying rate on I bonds is zero.
I bonds are not a short-term instrument like a Bask account it. It's apples and oranges. I think they offer a savings account paying 0.6% interest. So if you (a) want money with ready access and (b) think AA miles are worth more than 0.6 cents each, the miles account is a better deal.