For the main game, Minoriko tends to be better, at least, for a stay-in full-time healer. You'd want to use Reimu mainly for GHB or an emergency AoE heal.
However, in Plus, Reimu gets faster and faster, so the delay becomes less of an issue. Bosses start using obscene AoE nukes that Mino [Or, for that matter, Sanae/Eirin] won't be able to heal you from, whie the massive % equips, and numbers in general, will make HGB, and even Demarkation, heal stupid amounts. SP becomes less of a problem too.
Basically, in the main game, the best healer is Minoriko in general, but in Plus, especially as you get later, Reimu and Rumia overtake her. I'd say Sanae does too, since she can buff herself for bigger heals and more speed beforehand too.