I think this thought is common with a lot of home buyers, but I'd only recommend going that route after you've done the math.
Looking at bankrate now, it has the 15 year note at about a .6% discount over a 30 year: on a per month basis, for a $200k loan that's an initial difference of about $95 in interest per month - IMO a high premium to pay for the option of paying more with a 30 year, opposed to just getting the 15.
That is just the difference in interest paid with each payment. Still a good sized difference. I'm actually considering a 30-year this time for a different reason. We are at very low interest rates and I'm unlikely to see these again in my lifetime. So I could hedge increasing rates by locking in for 30 years.
A 4% 30-year mortgage payment is $763 / month
A 3.5% 15-year mortgage payment is $1,143 / month