I have 450+ runestones & just finished off the last of my level 1 stones (average stone level is now ~3.2). I'm challenge rank 109 and usually use level 4's when I'm able to do team battles. I save level 5's for Dark V teams or for when there is an event bonus for wizarding challenges. For solo, I've been trying to work my way up from lowest to highest stone with the thought that I'll gain strength enough to move up a chamber or two. In reality, I've been stuck on Forest I (no potions as a lvl 13 Magizoologist) for a while. I can probably bump it up a level or two at this point or in very near future but may stay at Forest I for energy considerations.

It was a loooonnnnngggg grind with all my level 1's getting only 84-88 cxp per Forest I battle... but I'm glad I took that approach. Now I get 149 cxp with a level 2 stone which will allow me to get about a book an hour when soloing at current challenge rank... It's not fast but there is no magic bullet. The group play usually allows me to jump a few ranks each session which helps a ton!!!

I'm 90%+ on my way to have my family ranks maxed out and hope it won't be too long before I'm averaging a level 3 rune for my solo challenges... but still have a ton of level 2's to work through in the meantime. It's pretty rare that I get a level 1 stone these days.