What is your favorite index fund? Do you diversify?

[Vincent Sottile]

I own VTSAX and plan to keep dollar cost averaging and hold forever. I've heard it argued both ways about why it is/isn't a good idea to invest in multiple index funds. What do you think?

I know many suggest an S&P 500 index. The REIT Index VNQ has also been on fire and it has tempted me to buy some and I know others suggest international indexes or investing in emerging markets (South America, South East Asia etc.)

So far I've been sticking to VTSAX, but should I consider diversifying through other index funds? Why or why not? Thanks!