If you don't plan to live there long then it is probably better to go with
ARM. But then again maybe renting is the best option.
ARM has two advantages: 1) most of the time, yield curve is upwards, ARM
rate is lower than 30-yr fixed, saving your on monthly payments; 2) because
of the lower interest rates on ARM, the loan is amortized down faster.
This means with same loan amount, if A takes ARM and B takes 30-yr fixed, A
pays less than B does every month, AND A owes the bank less than B does 5
year from now.
Now clearly ARM has risks, and refinancing is NOT free. If inflation rises
above normal which is highly likely, you would wish that you had locked in a
low 30-yr fixed rate. Again, if you are moving before long, it wouldn't
matter much.