I have mine structured like this:

• ~50% - ibonds - they've matured past the 1-year lockout period, so they're very liquid
• ~25% - t-bill ladder at brokerage (13-week t-bills purchased every 2 weeks)
• ~25% - money market fund at brokerage

My brokerage is also my main bank account, so it's really quick to transfer money to my "checking." In fact, I hold my t-bills in my "savings."

I'm probably going to sell my ibonds and either repurchase at the higher fixed rate or add to my t-bill ladder. If I did it today, I'd probably just go with t-bills.