For short term usage, go with a saving's account (shop around online, e.g. Ally) or CDs are the way to go. You don't want to take on market risk for something that may be used in six months (or even 10 years).
If 20k is really an e-fund, you could consider putting part in the market. Lots of us do (me included). The idea here is that if is really an emergency, I am willing to sell stocks during a down turn. Otherwise, if I lead a charmed life, I retire even richer. Roth IRAs and US I-bonds offer some nice properties for double use investments. With the Roth, after 5 years, you can pull out contributions if you need them. I-bonds are tax deferred until you redeem them (and then have some special caveats to waive taxes for qualified educational expenses and perhaps some other stuff). Worth looking into.
I think overall strategy and risk tolerance questions need to be answered before picking specific funds. If you push me I'll just tell you to get a Target Retirement fund (which holds a balance of stocks and bonds).