The advice used to be, if you can do 20%, do so, to save yourself that insurance expense (in the "used to be" markets, at least, where you ended up ahead, financially, by doing so).
P.S. Rereading my last sentence -- or, "sentence" -- I see that I definitely need one, or several, more cups of coffee.
There's also some incentives out there right now where the lender pays the PMI for you.
Since PMI is tax deductible now that makes it effectively less expensive, and avoiding it less advantageous/important.
The best choice depends on factors such as how long you will keep the home, but if you're putting less than 20 percent down, avoiding PMI is not a worthwhile objective. PMI might actually be the best deal.
I think I have to agree with my child co-commenters, that if they're waiving PMI in one sense, you're paying for it in another.
You always have to add up all the pieces -- over their respective lifespans -- and see where your total costs come out. As well, whether retaining more money up front and pumped into your own investments is going to outperform any additional eventual expense, allowing you net (and also considering taxes) to come out ahead.
Past a certain point, I'd say, make sure you're doing pretty well, financially, even if you end up leaving a couple of hundred or even a thousand on the table over the lifespan of the load. Instead, focus your remaining time and energy on having a good life. Worth far more than worrying about the last dollar.