Often, spouses name each other as their agent and often name an adult child as the alternate. However, there is no requirement that you name your spouse. If someone else, such as an adult child, would be in a better position to handle your affairs, which is fine too.
There is also no requirement that you name only one attorney-in-fact for all of your affairs. If there are particular assets (e.g., closely held stock) that would be more appropriately handled by a particular person, you can have more than one power of attorney to accomplish that by appointing what is referred to as a Limited Power of Attorney.
In Florida, as of October 1, 2011, it is recommended that existing power of attorneys be updated to utilize a new and improved form. The updated form requires the designator to specifically designate which powers are to be granted to the designee. Older versions of the power of attorney are still legally valid, but most banks and other financial institutions will not accept the older versions.