Army Reserve policy is to limit your deployments to 90 days abroad. Navy has no such policy so your deployment could be 6, 9, or 12 months.
The Navy has the Comfort and Mercy (unless the Mercy gets sunk in its battle with the Arizona). But they, imho, should play a very, very small role in your choosing a branch of service. There are a lot of good reasons to join the Navy, but the off chance of a tour on one of them would not be a big player among the many factors to consider.
There are a lot of good threads to help you choose a service on SDN, which will apply to the Reserve, to a proportionally lesser degree unless you get deployed. The big pluses for me for the Army for the Reserve Corps are $240k in student loan repayment (instead of $50k) and the deployment policy.