On your list, the "Fixed Income" category are bonds. There isn't one there that is short maturity. However, the reason MMM recommends short maturity bonds is that changes in interest rates don't have as much effect on prices. (If you have a 30 year bond that has an interest rate fixed within it, and interest rates in general go up, being tied to that low interest rate in the bond is much less attractive, so its price drops. The longer the remaining term of the bond, the more effect a change in interest rates have.) Since interest rates are so low now, its reasonable to expect the long-term rate to be higher than now.
Interest rates generally track inflation. (If inflation was to rise at 5%/year, a bank could make a profit on giving 4% interest. If inflation was 20%, the bank could easily offer 16% on deposits.) So, I think the bond fund on the list that would likely match MMM's underlying reason for choosing it is TIP. It's supposed to track treasuary TIPS assets which are tied to inflation.
For comparison, the investment types of the other ETFs are:
AGG - a broad range aggregate of bonds. It has both long and short term funds.
LQD - investment grade corporate bonds - "investment grade" bonds are safer, so lower returns, but lower risk of default. "corporate bonds" are issued by companies to raise capital.
HYG - high yield corporate bond - "high yield" bonds are riskier than the investment grade counterparts.
EMB - emerging market bonds - bonds sold to companies in or the governments of developing countries. Riskier, but with a higher rate of return.
MUB - mutual fund bonds - called "munis", they invest in bonds issued by state and local governments. The primary upside to these is that the interest earned in these bonds is typically deductible from state income taxes. Because of that, it typically doesn't make sense to buy these inside of a 401(k) or IRA. Also, some analysts think that those tax savings are already reflected in the price, so unless you make enough money to be in the highest tax bracket in the state, you likely won't see much benefit in these.
Good luck!
