Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.
At least for the size fish I'm most interested in... :)
(my interest) (trout) preferably at least 18", that stick their noses out, or boil on, aquatic insects.
BTW I'm responding at 1:15 a.m. because I'm all wired about leaving for Montana in about five hours for two weeks of great hatches and big rising wild trout. :)