Aura generation is based on the amount of "nature" about. More nature more aura nodes, and bigger aura nodes
So from my understanding of that, you'd want a jungle or forest biome
I'm not sure how BoP biomes handle spawning aura nodes, I'm sure they're around but I don't know if there's a distribution difference
Well that's actually why I'm asking to see if anyone actually knows since Biomes O' Plenty makes vanilla biomes a bit uncommon. There are certain BoP biomes that spawn a high amount of greatwood trees so I would assume they would produce a higher aura.
After a little research I did find that the enchanted forest in Twilight Forest does have an extremely high aura, higher than any vanilla biome or at least according to the chart I found (which didn't include any biomes from BoP). It would make sense since a large amount of silverwood trees tend to spawn there. I've decided to make my base there but once I unlock ze goggles of revealing, I'm gonna go around and see what biomes produce the highest auras and possibly record my results.