Since this thread is active, I thought I'd check in with a quarterly update. These comments reflect my personal preference and I'm posting mainly in case a newbie or hands-off investor might find their style similar to mine. To address the recent discussion, I think the Vanguard life strategy funds and Betterment are pretty much the same. I'm treating them the same, just commenting on my customer experience.
After taking a little time getting used to it, I'm really liking Betterment.
It's really easy to make monthly contributions, and I especially like the fact that it's organized by goals- I have three different stashes (goals) there- with different intentions (time frames for spending) for each stash. One "safety net" (60% bonds), one "conservative" (60% stocks) and one "moderate" (80% stocks, containing the bulk of my investment, for the longer term). On the grand total, so far I've made 2.5% since December 2013. To date, fees have totaled $6, or 0.04% of my total balance. I think Fees are charged quarterly? not sure, so far I've only been charged once, on April 1.
My Sharebuilder account is also ok. I'm comparing Sharebuilder to an account at Vanguard, and find the two pretty much the same. I like the Sharebuilder user interface and web site a little better (personal preference). I've also made 2.5% since December at Sharebuilder, with three similar sub-allocations to what I've set up at Betterment (VSCGX, VSMGX, MITFX). BUT I haven't made any contributions, because of fees that I'd be charged to do so. A point against Sharebuilder in that regard. But I like them because of their easy connection to my savings accounts at CapitalOne. Also a very nice web site. Vanguard may also have a user friendly web site, but so far, I'm not drawn enough by it to want to click around and see.
I predict my tendency will be to continue to make small automated monthly contributions to Betterment, and only occasional (annual?) larger contributions to Sharebuilder or Vanguard directly. We'll see if that holds in a couple of months.
I hope this helps somebody,