Welcome to the Ritualist Profession.
As to answer your question:
1) any can be good.
I have a Rit/Necro for several reasons:
a) MM (Spawning gives minions more health)
b) Corpse Management
c) I just love Necromancers
2) Why I love my Rit/N? I love Necromancers. See above. Ritualists can do just fine with Energy Management (Channellers can gain more energy than used with a specific spell; Boon of Creation allows you to gain energy and health for each minion and spirit created).
Ritualists can be global healers, heavy damage dealers, protectors, aid others with Weapon Spells, have have funny dances.
Monk Secondaries - too much healing; can remove hexes that Ritualists can't; why have even more hard rezes?; smites are okay; too much protection
Warrior Secondaries - tactics are good; don't bother with weapons; casting in an earthquake can be made uninteruptable I think (balance stance or dolak signet)
Mesmers - great energy management; good disruption; good health degen; make spells uninteruptable (except from falling); good cover hexes
Rangers - more spirits for spirit spamming; pet; disruption arrows
Elementalists - other elemental attacks other than lightning; added protection spells
Assassins - Teleports; Earth damage
Necromancers - MM; Corpse management; can have Energy Management with Offering of Blood (e); good health degen; good cover hexes;
Hope this helps.