I tend to use colored wool. If your making large mechanisms in redstone it's beyond helpfull. And if your making said large mechanisms its probably in creative mode so you don't have to worry about resources, even in survival if your to the point where you can make large redstone structures, you can spare a couple stacks of wool and dyes to make it so drastically easier to build circuits. If your not making circuits though I'd go with what ever fits, usually wood if its an external mechanism or stone if its some what hidden or internal. But in the end its really just what you think looks good.
And I mean like single/few blocks, not all the colors of wool
ex. properinglish's orange wool
Personally I think you'd have to be low on resources to use grass or wood for redstone
If there's an option not on here, please post it
Interested in pro redstone? Check out ORE at openredstone.org
Interested in pro redstone? Check out ORE at openredstone.org
Survival, whatever I have plenty of.