I have used McAfee SiteAdvisor for a long time and found it useful and trouble free... never used WOT and therefore unable to rate it.
There is another of these that is included in AVG 8 Free anti-virus. It also works well and seems to mesh well side by side with SiteAdvisor thus offering two opinions.
Bottom line is you probably will not go wrong with either of these. I will occasionally visit sites with a yellow rating but avoid like the plague those in the red category.
McAfee SiteAdvisor or WOT?
I have difficulty choosing the better one, please help me.