The intra day trading advantage has been mentioned....I will not repeat it.
One of the other main questions to ask is: what is your tax bracket?
If you are already in a high tax bracket, then you need to worry about two things:
+ Additional qualified dividend income, even though taxed at a lesser rate than income tax bracket, is still a tax.
+ Capital gains (both short and long term) can be generated which can lead to more taxes.
+ Capital gains can be generated even if you do not sell a single stock in the mutual fund...because somebody else sold their fund OR the fund manager did it.
In ETFs, you control the capital gains distribution i.e. no taxes until you sell the ETF shares.
For more details, refer to
http://www.bogleheads.org/wiki/ETFs_vs_mutual_funds.
I still chose mutual funds for other reasons that were more suitable for me...I do not have time to explain everything now...sorry. But if you have time, you can read my notes here:
http://humblefi.com/2015/01/24/mutual-funds-vs-etfs-some-links/. Caveat: I am not a finance expert.
Hope that helps.