We are not really in a position to declare any kind of standard transformation. It depends on a lot of factors involving the patterns in your data (uniformity and shapes of distributions and such), personal taste, tradition in your area, and what kind of effects you are looking for. Best recommendation I would make is to read the Results sections of RT studies that have achieved classic status and articles that focus on RT methodology. Here is a good start:

Fazio, R. H. (1990). A practical guide to the use of response latency in social psychological research. In C. Hendrick & M. S. Clark (Eds.), Review of Personality and Social Psychology: Vol. 11. Research Methods in Personality and Social Psychology (pp. 74-97). Newbury Park, CA: Sage Publications.