If you are not parading at your Home Unit, while on Class B or C, then you should opt for the option of going PRL and be administered by the establishment that is employing you. This way your Unit does not have a Posn Number tied up by a person who is not there, and they can recruit to fill those vacant posns.
Double Dippers don't have to belong to a Reserve Regt. They can still keep their Regimental Affiliation on PRL. As a Reservist, they can fill a spot in an organization, freeing up a Regular Force person for deployments. This is an ideal situation for a Annuitant, who now has settled down and doesn't want to be Posted again, at the same time, if they want to volunteer for a Deployment, they are easily accessible.
The only drawbacks with Annuitants, as dapaterson points out, are the Rules and Regulations dictating they can not work more than 360 days a year. They can plan a 35 day Unpaid Leave of Absence and collect EI, or break that 35 days up into smaller chunks (and perhaps not be eligible to collect EI). It is manageable if one so wishes.