Diurnal Sect
Benefic: 440
Helios: 330
Benefic II: 715
Aspected Benefic: 1144 + speedBonus' (110% × (200 + 6 × (140 + speedBonus)))
Aspected Helios: 660 + speedBonus' (110% × (200 + 10 × (40 + speedBonus)))
Nocturnal Sect
Benefic: 460
Helios: 345
Benefic II: 747
Aspected Benefic: 805 (115% × (200 + 250% × 200))
Aspected Helios: 431 (115% × (150 + 150% × 150))
Diurnal Aspected Benefic heals for at least 339 more potency than Nocturnal Aspected Benefic. Diurnal Aspected Helios heals for at least 229 more potency per target than Nocturnal Aspected Helios.
Most dungeon bosses shouldn't even really require more than five or six GCDs devoted to healing, thanks to the relatively low cooldown on Dignity. Therefore, Diurnal Sect is superior to Nocturnal Sect against most single targets and some small groups.
But if you're fighting anything that can do enough damage to break your shield within 10 seconds, like a deathwish-sized trash pull or a raid boss, Nocturnal Aspected Benefic's value increases because Diurnal Aspected Benefic requires four ticks to beat Nocturnal Aspected Benefic, whereas a fresh shield gives the full benefit every time.
Still this, though. AST+AST happens with fair frequency in DF, so it's good to know how to play both.