Interest only loans are stupid unless you are getting such a good deal that it HAS to make money. BE CAREFUL, because if the housing bubble burts, you are going to be FUCKED on an interest only loan. Left with a house that lost 25% of it's value and no way to get out of it.
DO NOT do an adjustable rate mortgage! Those four years will come up FAST and you will be caught with your dick in your hand on number 5. A lot can happen in 5 years. A friend of mine just had this happen to him. He planned to get out of it in four years, and got an ARM. His credit situation has since changed and he cannot refinance nor buy another house, and his ARM just kicked in raising his payment $500 a month! He is forced to sell now and move into an apartment, IF he can sell before he's in deep shit. Otherwise, its foreclosure time.
Do a 15 or 30 year fixed, it's the safest way.