I had Vanguard's LifeStrategy Growth fund through my employer, which is a simple 80/20 fund made up of total US stock, total international stock, total US bond, and total international bond. Pretty low expense ratio--something like .15. I liked it. Unfortunately my employer is no longer offering this, and Vanguard is automatically replacing LifeStrategy with its target retirement fund (with the retirement year based on the age of the investor, a crude and inaccurate measure by mustachian standards) unless we move our money into other funds ourselves.
As others have noted, the target retirement funds tend to have higher fees. I think it's weird and inelegant that to get close to the asset allocation I want, I have to choose a year that isn't actually the year I'm going to retire. And I'm not interested in a fund that rebalances itself every year on its own, because I'm looking forward to performing that annual ritual myself.
So I decided to buy Total US Stock and Total US Bond directly, with an 80/20 AA. The institutional versions of these funds are available to me through my employer, and the expense ratios are close to zero. I don't have any international exposure now, but after reading
JL Collins' thoughts on that, I feel comfortable without it.