Watch the Fingers Versus Pick online guitar lesson by Andy Aledort from Slide Guitar Power
Most slide players use a combination of their fingers and the flat pick for picking the strings when playing slide. Picking with the fingers yields a warmer tone and enables more precision in regard to pick-hand muting techniques. Using the pick will yield a greater attack and sharper, more pronounced tone, and one can easily employ many of the same muting techniques when using a pick. Personally, I like to utilize both techniques, often within the same solo. I'll usually start a solo by picking with just the fingers, and as the solo builds in intensity, I'll switch to the pick to attain a louder attack and more pronounced sound. I recommend that all aspiring slide players try both techniques to discover the advantages and disadvantages of each.