For holy it's complicated. There is many viable combinations, however I will keep it simple
For raid as log as you have any of these you are golden: Class ring / Ilterendi / Velen's / Maraad .... Prydaz also works but loses value outside of progression
For M+: Belt / Velen's / Maraad's (highly subjective and group dependent) / Sephusz .... depending on afffixes Prydaz is also nice, event boots are great on Dresaron in DHT for example.
My current setup is IIterendi+Maraad's (results in 47% crit, 47% mastery) for raids and Sephusz + Maraad (about 52% crit, 41% mastery) for higher M+ (I switch the back out for groups with 3 raged dps).
If I had to choose only two I would go with either Velen + Maraad or Velen + Prydaz since they will do you good service in both raids and m+.
Generally the only legendaries you really don't want to are the head, bracers, and gloves.