But since the last quarter of the 20th century (& even before then) the mayfly has had to make room for the caddis in the hearts of anglers. This is with good reason, as on many streams the caddis are a more important food source for trout than mayflies. In fact, in many places the caddis make up half of the trout's diet. Also, where many of the famous mayfly hatches occur for only a few days in the year, caddis hatches tend to go on for a lot longer - some lasting anywhere from ten days to three weeks!!
One of the biggest mistakes anglers make when fishing a caddis hatch is to fish it the same way that we'd fish a mayfly hatch. Yes, you'll catch some fish doing this (if your fly is correct) but not as many as you would if you studied the behavior of the naturals. One key give-away that trout are taking caddis is the the rise form. If you see splashy, loud rises where the trout might even leap from the water after a bug, it's a good bet they're after hatching caddis flies. This is because caddis don't stay on the surface nearly as long as mayflies. They come to the surface quickly, usually wiggle a bit, & "pow" - they're off. So the trout must be quicker to get them, hence the more violent & forceful rise forms. If you can get your fly to mimic the movements of the naturals on the surface, you'll be very successful taking trout.
If you're fishing a larva pattern, you want to fish it like you would a mayfly nymph - down deep close to the bottom, even bouncing off the bottom is very good. If you're fishing a pupa imitation, use it more like a wet fly by swinging it through an area of trout & letting it rise up as it goes, just like a real bug on it's way to the surface to hatch. In all probability many of those early traditional wet fly patterns were taken as rising caddis pupa by the trout back in the day.
In the end it doesn't matter which bug is better to the angler: mayfly or caddis. Look at & study the naturals on & in the water. If you can copy their size, color, shape, & behavior you're going to have success, no matter which hatch is on.