From my experience with ret pally. The best strat to be one is to be a ret pally when leveling, a prot pally when going into leveling dungeons and to be a healer at end game because your barrier to entry to be a ret paladin is being a ret paladin in raids. Once you got most of the good stuff, then it's an easy switch to be ret full time. However, if you want to further captitalize on gear, maybe consider going healer > prot > ret because prot tends to get a tiny higher priority in gear compared to healers and DPS.
The class is basically trade off central