I am currently trying to build a piston elevator in my single player world and I need about 200 blocks of redstone to complete it ("For the back wall"). I already have enough redstone for about 90 blocks but I think I could find more mining at a different level other that 11-12 (Which is the recommended level to find diamonds). If that is true I need to know what the level with the most redstone is. Thanks!
I've been doing some research on this myself, because, I need redstone, too.
I've found that levels 12, 13, and 14 are the easiest to mine in. You get about 4-5 stacks of redstone for every 36 stacks of cobblestone. If you count cave, then it's 6-7.
It takes about 1/2-2 1/2 hours to get it. Hope this helps!
Redstone will randomly spawn below level 16 at a 1.025% chance per block. There is no "Best level" because the generation is random. So, to answer your question, anywhere from bedrock to 16 blocks above bedrock should have an equal chance of being redstone. You can find more about redstone at the Minecraft Wiki page Hope that answers your question!
Judging by this graph of average block quantities the levels with the most redstone are 5-17.
Because of the high amount of lava below level 11 you would consider mining higher than that.