The main risk with an ARM, is that your mortgage rate and monthly payment could go up after the initial fixed period. You could reduce the potential impact of that risk by choosing an initial fixed period that is a little longer than your timeline. Also, make sure to understand the index used on your ARM so that you know what could cause your interest rate to go up or down in the future.
The main risk with a fixed rate loan, is that you're losing cash flow NOW in exchange for the chance of saving money at some point down the road if you keep the loan for more than 3, 5 or 7 years.
In either case, this is probably one of the most important financial transactions of your life. My commitment is to communicate and strategize with you every step of the way. Contact me for more info and I'll be happy to run the numbers for your specific situation!