The basic OBJECTIVE of an Emergency strategy is: To have 3 - 6 months of your budgeted income set aside in this quadrant to provide CASH for major emergencies vs. using debt for these type of events.
The basic CRITERIA of where to put Emergency deposits is: To have full liquidity and complete safety to your principal dollars. Therefore you should not be as concerned with a return on these deposits as you are to the liquidity and ease of getting to them when necessary. For example, a savings account, checking account, interest-bearing money-market account or even an H.S.A. is a great place to deposit these dollars.