I'm struggling with bonds myself, a bit. Until sometime last year, I never owned any. (Except a little as a checking account some time ago)
I don't like intermediate or long term, as I don't feel compensated for extra risk, with flat yield curve. And, yields seem low to me, so don't want to be too long term if they might go back up.
In taxable, I agree that 4% FDIC money market or an FDIC/credit union eq. CD on good terms can be sensible.
Another option is 4 week, 3 month, and especially 6 month treasuries from treasury direct, which can be linked to a bank account. Better rate than money market.
Or, Vanguard's short term treasury fund, which has a relatively high ER
or their TIPS fund, which has a longer duration than I like.
In a traditional IRA, ideally, I'd like to own short term TIPS (5 years maturity or less) but with my broker, that's not practical. Now I own short term treasury SHY, but the dividends are a nuisance. So, I'm thinking about one of the vanguard funds above, for the next bond purchase.