SPY vs Vanguard 500 index fund For IRA

[godoftrading]

Excluding the trading commissions to get into SPY versus nothing for getting into the Vanguard 500 index fund (VFINX), is there any reason NOT to go with SPY over the Vanugard s&p 500 index tracking fund?

SPY has slightly lower fees & it has the ability to get out at any point during the day which could be very useful in crisis times rather than having to get out at the end of the day with Vanguard.

Thanks for the advice.