I have been asked a couple of times for a quick shallow analysis of what ritual magics do what from the perspective of someone who wants to be a ritualist and is choosing a Realm.
Point 1 - assume that in Anvil you will always have access to one more level of lore than you bought, because you can go to the Regio (the ritual circle) and cast there for +1 lore.
Point 2 - nearly all rituals require a ref. A ritualist needs refs more often than anyone else but a very active priest.
Point 3 - you don’t need a Realm’s lineage or any of its magic to attend Eternal audiences, but you do need to be a mage.
Point 4 - get a mana site! Mana sites are a very good resource anyway, and ritualists eat mana like popcorn.
THE REALMS
Spring → only if you are already a physick and feel that that is not enough healing for you.
*Healing rituals are vastly efficient.
*There’s nothing else useful you can solo cast in Spring.
Summer → very strong, but purely combative.
*All the buffs are worthwhile.
*Cast 'em early!
Autumn → if you have a very particular ritual you are after.
*There are a bunch of really nice situational rituals here but the key word is situational.
Winter → if you plan on specialising in curses.
*A bit like Autumn, there are a bunch of fun situational things
*Some Winter spells are excellent. Some Winter spells have no discernible use.
Day → very strong and versatile, a midpoint between Summer and Night
*There is almost no bad Day magic, but if you do take investigative magic then nobody’s paying you to carry those mana crystals home - get investigating! 
Night → very strong, but purely non-combative.
*Some Night spells are quite poor, but most of them are hilarious, and all the best Night is soloable. If you’re on your own it’s really not worth taking magic that will hide your activities.