Advice for coding of factor levels consistently is equivalent-distant, centered on 0. So -1, 1 for 2-levels, -1,0,1 for 3-levels.

This a quote from Mark Bailey: Coding benefits the analysis in several ways:

- The parameter estimates are comparable.They are independent of the associated scale (units).
- The parameter estimates are interpretable. The intercept when estimated with real values is the response when all your factors are zero. What does that mean? With coding, the intercept is the mean response at the origin (center) of your design. The other parameters still represent the change in the response for 1 unit change in the factor, but in the coded space, 1 unit change is half the range. Double the estimate and that is the change in the response over the full range of the factor.
- The parameter estimates are uncorrelated or minimally correlated. This preserves power for the significance tests.

"All models are wrong, some are useful" G.E.P. Box