In my estimation given your timeframe, I-bonds make perfect sense. They've got built-in inflation protection, they're yielding more than CDs, and they're much more stable than other market products. You can only buy 10k per person per year worth of i-bonds. I'm assuming you're married? And if you have a kid, you're looking at 30k per year purchased.
You do make your assets illiquid for the first 12-months when you buy I bonds (ie can't redeem them within this period), but after that, they're very liquid, and you can just drop into a bank and pick up your funds. You do forfeit interest paid on the last 3 months if you use them within 5-years.
I'd be cautious with bonds/bond funds, or at the very least look at a short-term bond fund. They've never dropped by more than 10% or so in a given year, but with interest rates this low, it's hard to have a bullish perspective on them (not their purpose, anyway).
Stocks are obviously volatile. Yes, Netflix can go up by 500%. But that also means it can suffer a similarly disastrous decline. I wouldn't invest in something so volatile as individual stocks when you have such a short time horizon before you need the money. If it were my money, I'd shy away from stocks on such a short time horizon.
I see no advantage to a money market fund over i-bonds other than the money market is more liquid and acts as a better emergency fund (for the first 12-months). The only advantage to CDs is that you can purchase more than 10k per person per year.
