I am in the same situation with the housing loan vs. investments. I went to about 4 different lenders, local and online, and talked to them about possible home loan rates. Currently, I am 3 years into my 30 year fixed @ 4.375% which is a pretty good rate as it is. I was unsure if I should refinance with a 15 year, 20 year, or go back with a 30 year at a lower rate. In order to compare apples to apples, I had each lender give me a GFE (Good Faith Estimate). It is a standardized template that will help you compare apples to apples. If you dont get a GFE from each lender, then it will be hard to know what numbers you are really comparing against each other... So here is how it broke down for me:
Current @ 4.375%: $2300 (including escrow and PMI)
15 year @ 2.875%: $2700 (including escrow and PMI)
20 year @ 3.25%: $2400 (including escrow and PMI)
30 year @ 3.375%: $2000 (including escrow and PMI)
I could have swung the 15 year and cut the time it takes to pay my house off in half! BUT, That is a high monthly payment for me on top of electricity, water, garbage, groceries, etc and wouldnt leave me with much money at the end of the day to put into investments. So essentially, if i kept my current salary for the next 15 years I would have to hold off on investing for retirement for 15 years and basically lose that time for compound interest to help out my investments.
The 20 year came out to basically the same payment I have right now so I could live with the exact same habits I currently have (as far as spending goes!) AND cut 10 years off my home loan. It would have also allowed me to comfortably put in ~$300 bucks per month into an IRA on top of my company 401k contributions, and I could comfortably invest that money today...
With the 30 year I save ~$300 bucks a month from where I am at right now. So, this allowed me to now make my montly house payments AND invest $300 bucks per month with absolutely no change to my lifestyle. And, since I am currently able to make my house payment and swing $300 bucks per month into a Schwab account, if I take the 30 year then essentially I am able to keep my same lifestyle, make my monthly house payments AND put 600 bucks a month into additional savings for retirement (Schwab acct.)!! Thats $7200 bucks a year that I can invest, without changing my lifestyle at all. This is also assuming that I keep the same salary forever, which wont happen but its a worst case scenario.
In the end, I decided to refinance with a 30 year @ 3.375%. I would not have bothered refinancing unless I could save at least a percentage point. Reason being is that I am already 3 years into my 30 year loan so essentially I have 27 years left. By refinancing with another 30 year I am somewhat losing those 3 years of time. The other reason I wouldn't have refinanced unless I saved at least a percentage point goes hand in hand with the first reason. By the time I pay the closing costs, or have them rolled into my total loan value, not only am I losing that 3 years but I am also increasing the total loan amount by roughly 9k. If I were to just keep my current loan and make an additional 9k payment on my principal I could save a year or two of payments and interest which would have equaled the amount I save (this is assuming I was refinancing and saving less than a percentage point...).
All in all it took me a lot of chicken scratch on a paper pad, an excel spreadsheet with different amortization schedules on it, and a hell of a lot of back and forth and this and that before I decided on the 30 year. BUT, now I feel comfortable with my decision and feel like I can back up my reasoning. There are thousands of people out there who know more about money and future value of money vs. present value and all that stuff who would/will tell me I did the wrong thing. If I didnt spend all that time researching and somebody told me I did the wrong thing I would have started second guessing myself and thinking i eff'd up. So, spend some time, do some math, talk to your friends/family, and then choose a loan that you will feel comfortable with not only today, but also 10 years from now...thats my 1/8 of a cent