QQQ is top heavy on some stocks like Apple (11.55%...recently was over 13%), which is why it's underperforming for quite some time versus an S&P500 Index fund. It's great when Apple is doing great and a dog when its top heavy components are dragging. In addition, QQQ has a not so cheap .20% expense ratio.
http://www.invescopowershares.com/products/holdings.aspx?ticker=qqq
This is very true and more advisable IF one really focuses specifically on Vanguard Mutual Funds. It really depends on one's plans. But there are caveats.
If one wants to play different funds, Vanguard charges $35 for their Standard Plan versus $20 with Etrade. On NTF Funds, they charge you 1% if held less than 6 months. Also $1k-$3k minimum investment depending on fund.
Vanguard also charges a
$20/yr fee (waived if you put in over $50k)
https://personal.vanguard.com/us/whatweoffer/stocksbondscds/feescommissions
https://personal.vanguard.com/us/help/FAQBrokerageFeesContent.jsp#a
That $20/yr fee alone covers 2 ETF trades at a brokerage. If you invest twice a year, you break even with having an account at Etrade/Ameritrade vs. Vanguard. Also, brokerages offer free trades and bonuses when you open an account in addition to offering better services, research and free online investing classes.
If fees were an issue for a very frequent purchaser, you can program a mutual fund you purchase to automatically take money out of your checking, thus avoiding the fee.
Sharebuilder.com came out with a good product where auto investing is $4/trade or 12 trades for $12. That can be very desirable for the right person seeking this.
http://www.sharebuilder.com/sharebuilder/investment-options.aspx
There are no right answers and depends on the investor objectives and tolerable fees versus the competition.