Cell phones are good for non-emergency situations. The only problem with them in an extreme emergency, you have to dial the number, wait for someone to answer and then you have communication with that individual only.
With a radio. Just grab the mike, speak clearly into it your location and nature of distress. Not only will the CG hear your call but so will many other boaters, hopefully one will be close by and will be able to assist quickly.
Fixed mount over hand held because the hand held has limited range. Granted, you are in the bay and will probably have plenty enough range, but you will have to keep the battery charged and the radio will have to be with in easy reach to use. Fixed mount is pretty much install and it's good to go.