What dates? What rivers? Timing and elevation are both major factors in the size equation. Higher elevation means they reach full size later. They are full sized on the horn when they are just starting on the yellowstone, for example.
Mostly, I'd just go with sandwich foam and rubber legs. Yellow seems to work well, as does light brown. Tie yellow sallies and caddis, too.
If you're not sure on the wheres and whens, or if you're going to fish a few different places, I'd have them from an inch to 2.5 or so inches long. I am not the most experienced hopper fisherman, but in the times I've done it, pattern didn't matter.