@Robert Farris,
I am new to investing myself, but I think I can add some value to your question. I just had my purchase offer accepted today, and had to choose between the exact same terms you did.
I went with 15 years, and I'll tell you why.
Between 30 and 15 there was a $200 difference in payment per month, leaving me with either $600 or $400 in cash flow. I based it on a few things.
1.) I am currently 22 years old, and with a 15 year mortgage I will have to house paid for at the age of 37.
2.) Next, how much work does the house need? If it needs a good amount of things done, than the extra cash flow would probably be useful. If not, and you can afford the difference in payment from 30 to 15 that take the lower term.
3.) I feel like everyone here is failing to note that in the long run you will be paying a significant more interest and principal in 30 years than the 15. Yes you could refinance down the road, but if you can afford it and you don't need the monumental cash flow than pay it off as soon as possible.
As Ali noted, it depends on your plan, if its long term like mine by building equity and not being greedy with cash flow than 15 years is a no brainer.