IMO, damp finger (middle is preferred), synthetic head (rosined). I really don't use the thumb anymore because of the awkwardness involved in releasing a roll with a tap, or accent at the end. With your thumb, you have to twist your hand over to do this whereas with a finger, it comes naturally. This is especially useful if after a roll, eighth notes or other note values are needed directly after a roll. I know this isn't exactly what you are looking for, but hopefully it helps.