Skewing towards small-cap historically has had better returns (and higher risk) - total market gets you some mid-small cap exposure, and at Vanguard at essentially the same cost. VTSAX is something like 80% S&P500, 20% extended market.
Don't let perfect get in the way of good. Pick one and run with it. Since you're looking at non-vanguard funds, you might go ETF if that would ease your mind regarding the possibility of unexpected capital gains distributions.
I know we've been drilled to think that lower ER is the most important thing, almost to the exclusion of other factors. And at 1% or 2% vs. 0.1%, ER is a pretty big deal. 0.04% to 0.015% isn't nearly as big a deal. Vanguard funds tend to slightly out-perform the competition even at slightly higher ER's because there are costs that aren't included in ER, and that patent that terran mentioned.