I agree on the 1/4W, they seem to be the most convenient value to use. Higher wattage also aids in reducing noise, but I have not compared 1/8W to 1/4W resistors in any pedal to testify for a notable improvement.
I also use 0.6W resistors like these: http://www.musikding.de/Metal-Film-06W
I know they are more expensive than typical 1/4W ones found locally, but for a pedal it won't cost you much more. I usually gather things I want and order them to reduce costs. They are about the same size as ordinary 1/4W ones.